The fastest configuration would be GTX 470 SLI, followed by HD 5970 then GTX 480. In terms of raw performance, I'd go for GTX 470 SLI, if I were concerned with power or heat issues, the HD 5970 instead.
SLI or CF setup will produce a lot amount of heat, so if i were you, i would get HD5970 instead...
At 86c the 5970 isn't exactly an AC unit and in SLi the GTX470 seems to run cooler than that hot old ATi brick depending on which sites graphs are looked at.