I could understand changing out that 470 with it hitting said temps. Dude - hot stuff!!
I say go for it, but rethink your strategy a little: You've got a pretty decent setup now, and room to build very easily. Personally I would get a single 580 and a Phenom II 965 with a good cooling solution.
Get your CPU overclocked to 4ghz+ and everything running cool plus be blown away by a 580 and still thus have the option to chuck in a 2nd 580 down the line (unless newer fancy toys arrive)
Reason to do this instead:
1) your PSU won't handle 2 x 580's and your system (at least I REALLY don't think it will)
2) your CPU is prob holding you back considering your CPU is stock cooled thus prob not overclocked
3) the ability to upgrade your system more easily and more balanced now is within reach (2x580's will be severely bottlenecked by your current CPU setup)
And after seeing your edit above, perhaps you should invest in some heavy duty carpet cleaning (I'm presuming you have your case raised a good distance off the ground). Also remember you can sell your old CPU and 470. That's an SSD right there Edited by willibj - 3/29/11 at 12:39am