save a little bit, and get an HD 4870 or any nvidia with dual slot,
so you won't be adding heat too much in a case.
the 4870 runs alot hotter than even the 280 GTX LMAO, the only Ati card I've seen that runs at a cool 59 or 64 degree temp is the 4850 ICEQ4 which is 20 degrees cooler thant the reference cards.
ATi cards are one of the hottest cards I've seen running. Honest i'm still shocked to see that some people managed to keep the 4870 X2 soo cool, 45 degrees idle, mine stays at 50-64 idle and I have the AC on max sometimes!!!!!
either way if your going with ATI and you want a cooler card, try to add to ur budget a cooler. Personally I think it's pointless, heat never bothered me as long as it stayed under 95 degrees.
I think the video card heat will only be a problem if you have water cooling in ur system, which means less air circulation because of the cpu fan removal and the exhaust fan (even though you have a radiator exhaust, its just not as useful as a reg exhaust).