I would advise 2 Xeon 2687W's. These are octo core chips that have been around for a while and run at just above 3ghz with 16 threads. You can get them for about $700 each on ebay although in many cases these will be engineering samples and will have to select your mother board carefully for compatibility. The vendor can tell you which boards have been tested to work. I've had very good luck with supermicro boards.

If you get a m/b with 2 or 3 PCI-E gen 2 or 3 slots, you'll be ready for any GPU project that comes down the road. Expect to spend another $600-800 on the mobo. That's if you buy new.

Add a few more hundred bucks for a high end PSU, memory and large case. I would get at least an E-ATX and probably EEATX. Check case compatibility with the mobo.

Cooling options for server boards tend to be limited even though the 2687W's are socket 2011. The spacing doesn't work out well for very large coolers on dual socket m/b's so check that. But your overclocking options tend to be limited anyway unless you go with one of the EVGA boards. But they use a special form factor, so keep that in mind. (HPTX)

So all tolled, you should be able to build a rig like that for around $2000-2500 assuming you buy the chips and m/b used and the case, psu and memory new.

edit: btw, these chips have a TDP of about 150watts so expect the system to pull at least 300w at full tilt with no gpu activity. When I was running the cancer project I think I had 2 or 3 HD 7950's in the system as well and the total draw was around 500w IIRC. Just FYI.

That's a very good point. If you are going to focus on GPU work, you'll be less concerned with the capabilities of the CPU. That's not to bad mouth any AMD quad socket systems of course. You'd need to compare the bang per buck in terms of boinc points generated if you're going to compare systems based on CPU capabilities alone.

Plus I've always been a fan of AMD and would love to see them back in the race with Intel. It was just that when I built my servers, I had despaired of WCG ever getting a GPU project so I decided to try to go for the maximum power per physical core at the lowest price at the time which was about 18 months ago. I decided to go with several dual socket servers including the 2687w octo core. That was partly because of the hyperthreading architecture but also the high clock rates of those chips and the other hex and quad chips I was able to get. But I've always dreamed of having a quad socket machine. That's just not in the cards for me anytime soon.

I was actually about to ask if this would be possible, and am happy that it is. I might not be able to set a WCG Workhorse right now, but I'm looking to build one sometime in the future (Maybe a few years from now).

If you have trouble setting up the 4P with Linux, shoot over to our forums. We have quite a few members with quad sockets and Linux that could probably give you some assistance.