Originally Posted by Sychodrama
470s pretty well outperform 460s
I agree with that. The 470s are a beast.
Also, to answer your question, I have no switched to tri-sli 580s.
They run so much cooler over the 470s, even at tri-sli or single cards.
The 580s idle at 32c and peak at 69c in benchmarks on air, in a case with not that good air cooling in it.
My 470s used to idle at 55c and peak at 95c.
Raw power wise:
The 580 is a real beast of a card, and very well cooled and performs great and overclock better.
And as a single card, you will not have issues with games which don't support SLI well, and much less stuttering while gaming.
The 580 will not out-perform two 470s in my experience.
So if you are looking at raw power, its 470s. If you look for cooler, less issues, and less power hunger, get a 580.
Also, it depends on your budged, since I guess you will lose some money selling the 470s and buying a new 580.