Hey all,
 
I'm looking into upgrading my CPU and associated parts. Currently my system is:
 
CPU: Intel Xeon X5650 OC'd to 4Ghz
Motherboard: EVGA X58 SLI
RAM: 12GB 1333mhz OC'd to 1450Mhz
Cooler: Corsair H100i
Graphics Cards: 2x EVGA Titan Black SLI
Storage: 1x 512GB Samsung 850 Pro SSD 2x 64GB OCZ Agility 3 in RAID 0 1x 1TB WD Black Drive
Powersupply: EVGA 1000G2
 
Now I'm not sure how i should go about upgrading. I have a MSI z170 board lying around with a bent pin my friend gave me that i could get working, but I'm also wondering if I should go for the new 6 core i7 8700K, or an old x79 or x99 platform build? 
 
Thanks in advance!

I think ita good to build in the current generation of intel platforms, otherwise your "new" system may be short lived.

Is there a reason you feel the need to upgrade?
What do you do with your system? Any special programs you run? What is your budget?
 
That hexcore at 4ghz and the two Titan blacks should play just about anything you throw at it.
The Titan blacks are worth a few bucks to people who do BOINC and other DP workloads.
That MB and CPU 150$, the two GPUs 300 each maybe more. Memory 60-70$
Thing is now new GPUs are up there in price, but seems EVGA has some stock more often now. But prices even there are up. May have to buy a bundle, GPU plus a CPU cooler or something. You want a good cooler the the new CPU anyway.
 
I can say the z370 and i5-8600k hexcore can be had for 350$ or so in a bundle from newegg, and it is a real sweet CPU. Got that with the Asrock z370 Killer /AC nice fair priced MP, 16gb Corsair DDR4-3000 for 520$
Six real cores no HT but can hit 5ghz or close to it. DDR4 memory is starting to comedown 16gb 150-200.
All depending on brand and speed. I would go DDR4-3000 or better.
I do believe the PCIE run at 8x8 gen3 when both slots are occupied, should not be an issue.
 

MSim
I wouldn't waste anymore money on the X58 platform. The first thing i would do is some research to learn what features the top mobo mfg offer. That way you can see what's available and what you want. That is what i did last year before i purchased the system in my signature. 
 
The top 4 motherboard mfg (ASRock, ASUS, GIGABYTE, MSI) all give you more/better features for the money. If you will be using onboard sound, be sure to check out the mobo detailed audio specs and look to see what features the audio software comes with.
 
ASUS has Aura eco-sytem, where it's RGB sync software can work with a lot different RGB hardware on the market. If you want to crazy with RGB, that is something to consider.
 
 

That chip oced though is sleeper...probably shouldn't throw money at it either I agree. Thing can still do a lot of stuff though.

jfw06013
It's funny because I bought a 6850K cpu for my EVGA X99 FTW K motherboard and the only real difference is that my ( 6 year old) i7 980x socket x58 ( ASUS Sabertooth) is the instruction set (cpu) and the cpu uses 10 watts less than the 6850K.
And the X58 PCI-E is not that much of a bottle neck.
I am using a GTX 1050Ti video card on a AOC AGON 35" monitor, I do have some minor problems with the monitor as I am using a HDMI cable that came with the monitor and it's only going with the default 50Hz instead of the overclocked 100Hz.
Even so in the game Call of Duty at max setting, no tear, so I am using this machine as a test bed for my EVGA FTW K so I have all the kinks worked out (I am using at least a EVGA 1080 Super Clocked video card in that computer).
 
I'm looking for a a cable for this monitor that has Display Port on both ends because HDMI will not do it (100Hz) .
So any suggestion (web sites)  that have a good quality cable will be appreciated.

Yeah waiting on FTW K another one replacement to get back rmaed. I doubt there is nothing wrong with the 7700k. should boot right up.  And hopefully didn't kill the Chip with the Delid/Relid job done the other day, should be some interesting Results.  I'm betting will run a little cooler even with Mx4. Now if it don't boot up gotta be the chip..cause I already tried some different ram and was the same thing. 
 
And the gigabyte suppose to get back too next week, there was some Bios corruption on it, said they fixed it. And looking at a Cool Supermicro's version and take on the Z270...kinda really want it too. 
 
so back up has been Piledriver and the x5650. Need a better board for that chip though the ones that can clock it..the sabertooth can and think the U3DR can and a few others not too entirely sure. 

Agreed, with a side note, overclocking can still help increase performance, as well as tightening the ram timings, that can really help too (by a few percents but it still helps)