If I was to chose it would probably be the 460s in SLI (only two can be put in SLI as it does not support 3-way on the graphics cards themselves), but they would have to be the very best 460s which at present time you have two differents good ones to pick from:
EVGA GeForce GTX 460 FTW 1024MB GDDR5
This is the new generation type of the 4000MHz memory clock 460 which has came out very recently, this is the 460 which now has the highest specifications in comparison to the other 4000MHz (memory clock) 460 graphics cards. The only dislike I have with this is that you could arguably use a better GPU cooler.
Gigabyte GeForce GTX 460 SUPER OC 1024MB GDDR5
The first of the 460s that I saw which had the 4000MHz memory clock and is the second most highest spec 460 (with 4000MHz memory clock) despite the fact that it was probably one of the first 460s to be released with it's types of memory clock. The difference between this and the EVGA 460 is very little and with overclocking you might be able to match this card to the same spec as the EVGA graphics card. However, my personal like of this is its twin fan GPU cooler which is known to run silently while keeping the card cool too.