The hot air is spread out. Have a look a this
http://event.msi.com/vga/twinfrozriii/index.htmlSo a some hot air is probably pushed towards the back. But if you look at my screenshot of a couple GPUs doing 59C and 66C, I believe it'll be fine. I think the other GPUs with higher temps need a TIM replacement. From reading the newegg.com feedbacks, the Twin Frozr 3 have bad TIM from the manufacturer. Once I get around to getting it replaced, I'm sure I could lower the temps quite a bit.
Are you all really sure about the "cooling"? The 7950 blows the hot air towards the BACK of the cards.
So in this rig all the hot air is blowing out downwards to the table and if I see right directly to the PSU. And because hot air rises I think you have the problem, that you
a) blow the hot air out
b) and that the hot air rises up again in the direction of your cards
But maybe I am wrong. At least with my 7950s the air is blowing out to the back.