Originally Posted by slaWter
Have you considered running Tesla cards instead?
That's another option. But that would be a very large price tag for 8 high end Tesla cards, which typically cost twice as much as their GeForce counterparts. And the capital investment has already been made, so it'd be a pain to sell/buy all the cards.
The only real performance difference between Quadro cards and the GeForce "equivalents" is the double precision floating point performance. There are some bandwidth discrepancies too that can be addressed via BIOS updates.
This may seem like a silly question, but have you looked at other people who run the same or similar setups? What OS do they use?
Also, was this setup purchased or assembled? There are vendors that sell computation rigs like that with multiple GTX 580's. Do they support Windows? If so what version and how many GPU's are they using? Another option to consider is scaling back the PCIe width on the cards to 4x or 8x (if they aren't scaled back already, which they probably are).