Hi folks.
 
I have an SR-2 and a pair of E5645 CPUs. I also have 12x 4GB DDR3 1333 ECC Reg and 8x 8GB DDR3 1333 ECC Reg.
 
I'm interested in using the board to run FreeNAS using ZFS to handle a substantial number of disks, so need lots of RAM and not a huge amount of CPU power.
 
Can someone please advise if this is worth attempting? I am looking for low power consumption overall, so reducing the CPU clocks seems like a logical step to me.
 
Thank you!

If you have power management enabled (SpeedStep), and have everything running at stock clocks the advantages of undervolting, underclocking and disabling cores will be relatively minimal, as when the CPUs aren't under load they will clock down and undervolt anyway, that's what SpeedStep does.
 
Regarding RAM, I think you cannot have 8GB+4GB in the same bank, but other than that, various combinations might work. Note that once you start using 8GB DIMMs you will need to make sure you have appropriate DIMMs and follow all the advice on the threads regarding running with 96GB of RAM. If your DIMMs don't fit the spec described on the other thread, it most likely won't work, and even if they are, the results are sometimes hit and miss (e.g. more people are reporting success with higher end CPUs than with lower end CPUs).
 
Note that the SR-2 has various stability issues with SAS controllers (I have tried two LSIs of different generations, an Adaptec, and a 3ware, and all have lead to lock-ups under certain circumstances). If you are absolutely stuck with using a SAS controller (as per what is in your signature) and switching to SATA is not an option, make sure you at least disable VT-d in the BIOS, and seems to improve stability, but I haven't tested it extensively because I absolutely need VT-d (my SR-2s are multi-seat virtual workstation).
 
One other word of warning - if your machine is going to be up 24/7 make sure you have monitoring and alerts set up using lm_sensors for the NB fan rpm. They are quite crap (standard cheap DC fan, not ball or fluid dynamic bearing) and are prone to seizing up. Make sure you use dust-filters on all intake fans on your case, and tape up various grilles and vents not occupied by intake/exhaust fans. And even then schedule extensive hoovering of the dust out of the machine at least every 6 months. Note that it is nearly impossible to get the dust out of the NB fan heatsink just by hoovering it, the fin design is such that dust will get quite thoroughly stuck in there and won't budge unless you take the top cover off. Running with dust filters helps alleviate the issue.

EVGA do PSUs, you know, and they come with 10 years' warranty. I have a 1300W on one of my SR-2s.
 
As for the rest of it, I am going in the other direction - consolidation. I have virtualized most of my machines onto my SR-2, including my gaming systems. 12x 4GHz cores has thus far proved sufficient even under two concurrent gaming loads - it is actually quite difficult to consume that much CPU under non-synthetic load conditions. My other SR-2 is purely a mirror for backup purposes and only comes up every day or two for a few minutes to zfs receive incremental snapshots from the primary. The only reason the backup is also a similarly specced machine is to make it a quick and easy drop-in swap should the primary suffer a catastrophic failure.

LOL! There I was advocating using fewer machines, so off you went and acquired an extra one. :)

Import them? Why? Scan, Ebuyer and many other UK retailers sell them.
Be careful with the assumption that it is the same PSU just because it is made by the same manufacturer. That really doesn't follow at all. Also, do Super Flower offer a 10 year warranty on their PSUs? In my experience, PSUs are the second least reliable component on any system, right after HDDs.
 
Cooling is seldom a limiting factor. You are going to be limited by the FSB before the temperature with a reasonable HSF. Expect to not be able to exceed 180 bclk reliably (PLLs destabilize and there's no voltage tweak that will get them stable past that, you'll see clock frequencies spiking all over the place). Personally I would not go past 177 bclk because that is how far you can go with QPI set to 4.8 without exceeding the 6.4GT/s spec of the CPU and NB. There really is not much headroom on the QPI. Also you will likely need to adjust your uncore, as that starts to destabilize at around 3.4GHz (on Westmeres the default multiplier is 20x, IIRC, not sure about other CPUs). I am running 166x24 on air with HR22 coolers and I cannot exceed 70C even when running minerd --algo=scrypt --benchmark or hours on a warn day (well, as much of a warm day as we get in UK).

Scan seem to be listing at least 4 different 1600W EVGA PSU variants at a quick glance (not sure it really is 4, but the point is they are listed by UK retailers, Google "evga 1600w").
 
And I wouldn't be saying that PSUs are the 2nd least reliable part if I didn't see them fail regularly.

Could be an artifact in your measurement due to a small sample.