Probably would impact life but to be honest in 4-5 years time the card would be obsolete and junk. I wouldn't worry about running temps too much. The power bill and cost to air condition the room is probably more significant.
As far the ATI 5000 series. They have eyefinity which I find pretty nifty. Better than Nvidia which offers nothing to match. Then again I won't give it too much merts because dual monitors have weird aspect ratio and most games won't support that.
If you are into Eyefinity, go for ATI. If you don't care go for the GTX 470. I just can't recommend the GTX 480 because it is over priced. Get the 5870 if you want something better than the GTX 470.