I'm putting together a general list for my first system build, and I came across the little tidbit that the GTX 470/480 idles at around 70-80c running a dual monitor setup. I was planning on getting a GTX 470, and was wondering if running the card at those temperatures constantly is going to impact the life of the card by a significant amount, and if those high temperatures should be enough to push me towards a Radeon 5850/5870, which run cooler with two monitors. Also, since from what I read the cards just run at a very high capacity with two monitors plugged in, will the temperatures still increase much when gaming on a single monitor?
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.