... that has a large rear-mounted fan BELOW the video card.
Heat rises, so it shouldn't be above
the video card?
Good question. The cards I have vent some hot air through the second PCI vent, and a lot more into the case below the card. Besides there is already a 120mm fan above the top card on most cases.
This system (whatever it turns out to be) will have huge amounts of air in and out, it won't have much time to rise.
On my SLK3000B/8800Ultra combination, there was an extreme "hot pocket" below the video card, and convection and two 120mm front input fans (one in a Kama Bay) and open PCI slots didn't help it a bit. The temp sensor on the lower part of the M/B was reading higher than my CPU!
I tried one, then two of those useless PCI slot fans. The first one brought GPU temps down from 99-100C to 95C, the second to 94C. Then I pulled them and I strapped an 80mm gaming fan across all the PCI slots. That fixed the problem.
A fan blowing perpendicular thru the back of the card (in the HD bays or something) should suffice, as with my 4850 w/S1.
Yeah but I am talking nVidia cards here...
Oh yeah, I am open to some case modding.
Get a top PSU mid/full tower case and flip it
I am seriously considering that. I would do it with my extra Three Hundred except there's not much meat to work with if I leave the P/S at the bottom. I'll be splicing sheet metal instead of just re-riviting it. Still, I may try it. It's only $50!