The game is gpu extensive. I have to play with an open case and two extra fans (ati hd6950). The AA gives the heaviest impact on fps and still looks terrible. On my system it cuts to a third (no aa 60-70, full aa 20-25). I also turned off the shadows to go easy on my ati card. It's still hot but doesn't crash anymore.
Thanks for the tip, I'll try and do the same.