Quad monitor setup crossfire

I actually did assist in a little research a few years back in medical imaging, though I was focused on the image acquisition side, while another post doc in image processing handled that with his own machine in his lab. This simplified our requirements since our system only needed raw CPU power which was best handled by dual quad core Xeon's back in the day.

An i7 975 is probably more powerful than the system I used to work on in the lab, but since you are already waiting on the 5870x2s, it shouldn't be too much longer of a wait until the Gulftown based i9's with 6 physical cores is out, Q2 of 2010 are what the current rumors say. These at least will be compatible with the X58 boards, so you can start shopping for boards and coolers now. As for the rest of your build, I'd probably keep tabs on what the prices on Intel 25-m SSDs are, and 2TB hard drives, but prices may be vastly different later on than they are now.

I know you mentioned that your project is grant money funded, but that's still no excuse for wasting it without need. We had a nicely sized grant and wisely spent maybe $7,000 on the workstation when we could have easily spent $12,000. When it came time to build the custom designed 3D axis imaging arm capable of 5 micron steps, the additional $40,000 nearly finished off the the funding before we got results

It really comes down to what you need your GPUs to do. If gaming was your only need, even just a single 5870 is powerful enough to drive 6 monitors to render a single game, look at the tech demos for ATI eyefinity for more details. If you were simply just displaying images collected and pre-processed by your 3D imaging system, I'd say you wouldn't need too much more power. However, if you will be using this system to create realtime renderings or, construct the actual images, you will need more power, and that's the type of tasks workstation class GPU's excel at. That reason alone is why those cards like the latest NVIDIA Quadros or ATI Fire GL cards can cost $4,000 just for a single card.

To split the difference so to speak, I think you're on the right track with 2 5870x2s. If you scale up to 3, if it's even possible, power and cooling demands will become a liability, and you may end up with a finicky system that will need routine maintenance to keep running in top condition, when I'm sure you have more important things to do with research and development, or some sweet gaming during downtime.

As for your power needs, I see no reason to go any lower than the 1000W, if you plan on adding and upgrading to this system, you'll need plenty of growing room. There isn't a whole lot of selection out there for the kilowatt and up PSUs, so I wouldn't restrict yourself to just modular ones... for production or other highly demanding applications, continuous cables are preferable. I think Corsair has recently released a new monster of a PSU, larger than their 1000 Watt units, not too sure on details at the moment, but that would probably be a good one to look at. Seasonic, Enermax, and the high end Antec ones are also possibilities to look at.