A 4.1 over-clock is probably a sure bet 24/7 anything higher just depends on the chips you end up with. If you could do a  geekbench 3  benchmark with your current system and post the results I could tell you what to expect from a dual xeon sr-2 system.

Here is a screen with the 8 detected processors.

If I choose 6 cores the numbers start to rise 17176.
 

2 logical processors drops to 4k, 6 gets the highest for me. so that benchmark version 4.2 is optimized for older cpu's.

@cuda-dude: I forgot to tell you for that benchmark, disable HT. The speed should be much higher now. What do you get?

Also I don't have time right now to clock my system up which would improve the scores, my system is pretty stable at 4.3 I run at 4.1 because my temps are down at 25-32c. Also at 4.1 my memory is running at 800 where it should be and my system runs smooth when I go past 4.1 I have to set the memory divider and my ram drops off in performance and I have to go to 4.3 to 4.5 to get it back near it's rated speed. Then it becomes unstable as one of my cpu's is better than the other. One cpu needs lots of volts to run at 4.3 and the other does 4.5 on moderate voltage, I have just not felt like spending $400 to maybe get another cpu as good as my best one.
 

Main thing is to get your hands on a good working SR-2, the xeon prices are falling right now x5690's on ebay are at $383.00 so $1300 for a running complete system that you can upgrade the xeon's on when they come around for a good price is a great start. I follow  the prices pretty close and $400-$800 depending on having the backplate and all accessories is the current board price right now.

I just noticed your sig. says E5690 x2...is that what you have or is it a typo and should be X5690 x2? And $400-800 is just the SR2 you're talking about right? I think on the new system the SR2 doesn't mention the backplate in the description so I guess I wouldn't get one. Do I really need one?
 
I'm sure the used system has it as it's a ready to go system. Oh, and if you're getting almost the same benchmark as the used system then I don't think upgrading from X5650 to X5690 makes any sense. What's the fastest cpus I could put in there? I doubt it'll be significantly faster and definitely won't justify the minor little speed boost for another $800 maybe (for 2x cpu).

Then I guess $1300 for that used system is pretty good right?

I was thinking, if I was to upgrade the two air heatsinks I mentioned to say H100i or something, would I get much of an improvement in OC? Probably not much eh, maybe go from 4GHz to 4.1Ghz?

What would be normal temps if I was to stress test it for a few mins (Prime95)? This'll be 24x7 operation so also let me know what temps I should not going beyond. Is 75C normal and OK under 100% load, with maybe 80C being the max?

Well the other system I have to order and then build and after all is said and done I think that'll cost me much more as the $1050 means I only get the 2 x5680's and sr-2. I'd still have to buy a case, ram, video card and 2 coolers. I'm pretty sure that'll be much more than $1300...probably closer to around $2200. Of course it'd be a new system with "slightly" faster cpus that may or may not overclock well...and anything under 4.2 GHz isn't all that impressive as I'd get with the used 4 GHz system. I think the used system makes more sense. Of course if the x5680's would give me significantly better performance it'd then be worth it.

Very nice and i like what I see in terms of the numbers however I doubt I'll be lucky enough to hit 4.6 or 4.75 GHz on the SR2 with 2x5650's or 2x5680's. Yes, the 5650's are very cheap but I still have to spend $350 for a new SR-2, another maybe $200 for a PSU, $400 for a case that supports the SR-2 (thinking Obsidian 900d) and ram...I don't know how much but I'm guessing $350 for 16 GB. Plus about $200 for used 5650's after shipping and customs. That totals $1300. Then I still need 2x coolers...though I'd probably use one of my used H100i's and then buy one new one for $130 giving me a total cost of $1430...and again, I'd probably have to be very lucky to hit 4.5 GHz stable 24x7...and likely only 4 or 4.1 GHz is expected.
 
You got good results because of your high overclock but I can't expect to get anywhere near those numbers since I'm not likely to be as lucky overclocking my used 5650's or 5680's that high. Then comes the huge power draw like you mentioned, costing me more every month when my electricity bill comes in.
 
So I think the cheapest and safest for the most performance would be a 5960X. Only one cpu and performance is nearly that of 2x X5680 with an SR-2.
 
By the way, chess engines nowadays will use up as many cores as are available. The Fritz benchmark may not be that way but stockfish, houdini, komodo they all will use whatever cores you have. I'm surprised you were able to get 12 cpu's detected with the fritz benchmark. Two people I asked to run it both told me only 8 are detected for them. What version is that?
 
My goal is to get the kind of numbers you got for the cheapest and most likely success at succeeding at reaching this goal. I'd be very happy with 23,000 kN/s using Stockfish as I only get about 11,000 with my 3930K at 4.70 GHz. With Houdini 4 I get about 20,000 kN/s.
 
So now I'm not sure which way I should proceed. 5960X still seems the best likely-hood of getting close to that 23,000 if I can OC it to 4.40 GHz at the lowest price....but I've always kind of wanted my first XEON system so I'd kind of prefer to get that instead. I just don't like the extra cost involved and that it's pretty hard to OC them with the SR-2. Double the coolers too...if I knew I'd get stable 4.50 GHz and near the same numbers as you posted above I'd go for it. Unfortunately I usually struggle when it comes to high overclocks...eventually I'll get a reasonable OC that I'm happy though. But even with my 3930K, usually stable 24x7, I still get black screens every now and then if I run the engine for over 12 hrs at one position but that's rare. I could lower the OC but I just don't like the sound of 4.50 GHz :-)
 
Like I said...I could go with the $1300 used 2x X5650 system that's all built and comes complete with case, psu, 24 GB ram but he's only running it at 4 GHz which leads me to believe he can't get much higher than that, stable at least.  What would you do? Highest kN/s is the ultimate goal...and I'd like to keep the cost around $1500 CDN.

Why would you need two PSU's in a case? How does that benefit OC'ing, or is it for a different purpose?
 
I hear what you're saying about core scaling. I don't really know about it but I can imagine it could be an issue. You seem to really like the SR-2 however you haven't really answered my previous post about successfully OC'ing the 5680's and/or 5960X . You also say you wouldn't go for the SR2 now that you know what you know but you also don't say that you'd take the 5960X system over it so I'm still confused.
 
Also, the H100i, while it doesn't cool as well as the Nepton 280L you recommend, according to user comments and reviews it's also louder...and I already think the H100i's are loud...especially since it's in my bedroom.
 
So straight out, do you recommend the SR2 with two OC'd 5680's (@ hopefully 4.5 GHz) and two Nepton's 280L as the ultimate chess pc? Or go for the cheaper solution that's almost the same performance and go with the 5960X? Or is there something else even better that doesn't cost much more bit still gives you better performance (in case I missed it through my research so far)?

A dual e5-2620 v3 is only 2x2.4 GHz while a dual x5680 gives me 2x3.33 GHz which is almost a 1 GHz difference. Also, the difference in benchmarks is quite big so it doesn't even look like I'd get anything CLOSE to the 23,000 kN/s you got with your dual x5675's which is what I want (or better). 
 
And who knows what OC I'd get on the e5-2620's...and what board can you overclock those with anyway?
 
Same goes for X5680's...while they're "capable" of 4.5 GHz, who knows if the cpu's I'll get will get me that kind of OC unless you're saying 4.5 GHz is about an 80% chance or is average and from what I read 4.0.4.2 GHz is the average...it'd be more expensive sure, but again, I can pay a little more if it'll give me even better kN/s than what you got. Won't the 5960X OC'd to 4.5 GHz give me almost the same as 2x5680's OC'd to 4.2 GHz? According to the link below, yes. And a 5960X setup would cost me much less:
 
http://www.sedatcanbaz.com/chess/?page_id=287
 
Also, I don't know how you got 23,000 kN/s with your dual x5675's when the link below shows dual x5680's is about a 19,000 kN/s average.
 
http://www.sedatcanbaz.com/chess/?page_id=19
 
And actually, you said earlier "X5650s are very cheap and give you at 90% of the 5960X numbers. I payed USD400 for a pair of X5675s, but USD150 for a pair of X5650s sounds smarter." According to the benchmark above, dual X5650's will give me about 12,500 kN/s at 3 GHz...are you saying I'd get about 22,000 kN/s if I could overclock them to 4.5 GHz? If so then that $1300 used system with dual x5650's would be good, except the problem is the max. overclock on it is 4 GHz which is likely going to give me less than 20,000 kN/s in SF.
 
The last screenshot you posted looks like that of a dual X5690 setup (not 100% sure since screenshot is a bit small even after clicking it). Is that your setup, or one you used to have? 4.90 GHz is an excellent overclock and I don't know what coolers were used for that but with my luck I'd probably be lucky to get 4.5 GHz on the SR2. Regardless, that setup is out of the question for me anyway since I can't afford 2 of those cpu's at $1700 a piece...although they are going on ebay for about $600 a piece to my door. But I don't think it'd be much faster than 2x5680's or even 2x5650's...since unfortunately there's no chess benchmark with dual x5690's.
 
cuda-dude has a 5690 setup but his fritz benchmark is only 20,000 kN/s. I get 19,000 with my 3930k.
 
Hmm, I found a pair of x5690's on eBay that'll cost me about $1150 CDN at the door. It'd be nice if cuda-dude or someone would run the Stockfish benchmark so I could see what speeds I'd get with that pair. If a bit better than yours I'd probably go for it...then buy the SR2, ram and either H100i coolers or go with your Nepton suggestion...although that one is quite loud over the H100i.

i am having trouble with direct links here.  try h t t p //hardforum.com/showpost.php?p=1041124886&postcount=1307 for a better version of my screenshots. or i can PM you a teamviewer login on my machine so you can have a nerdgasm of chess power. A X5675 using turbo bin run all cores at 25x, just like a non-turbo X5690, so i really don't see why my results look out of the charts. sedat hasn't responded my email nor updated the charts, but since i have multiple runs using lower voltages, i don't mind repeating the session with a video live feed .
 
about the e5-2620 v3 suggestion, the SR2 can go head to head with the current chess champion  Xeon E5-2697 v2, a beast with 24 cores and 48 threads, i don't see how the lower cored and slower 2620 v3 can hope to compete.
 
These are enthusiast builds, single thread performance remains relevant, which is why the options are SR2 vs 5960X. 
i will try to consolidate the build info on hardforum, which is friendlier to my images and links than here, but i do recognize that was EVGA's forum that provided with the important solutions to RAM selection and how to Turbo.