460s aren't very hot, there has been some issues with them lately however, a lot of people are reporting blowouts on the cards about 8 months after use. This is due to the heatsink not directly making contact with the chips after the pads have worn out, at least to my understand.
However for performance GTX 460 SLI will outperform a single 570.http://www.anandtech.com/bench/Product/314?vs=306
We won't know what write for you though unless we know the rest of your system specs. Particularly your PSU, Mobo, Resolution, and PSU.