I have just SLI 2 x GTX 460 1GB, granted mine are super overclocked versions running upto 930Mhz, I'm not sure which versions you have - the performance is above GTX 570 and somewhere around GTX 580, insane
around 110fps on BC2, 1920x1080, 32xCSAA, 16xAF, HBAO enabled, i.e. all settings at max
you'll be wanting to play (is this for gaming?) at 1920x1080 (1080p), the SLI GTX 460 or single GTX 560/560 ti will handle this res no problem
my impression would be that if you live in a hot place and have a computer like the ones we're talking about you will also have air conditioning machines, god I hope so anyways
the 460 do run cool - mine idle 27c, max 59/60c (bear in mind i live in the UK where it is not warm generally), I understood the 560/560 ti run higher temps, can anyone comment on this - I shouldnt imagine the temperature difference is huge either way
does the mobo have the correct number of lanes and is SLI ready?
and do you run any PCI (or other) cards that might have to be taken out when you install the 2nd GTX 460 (i just made a dumb error, purchased PCI sound card and 2nd GTX 460 at same time - the 2 x GTX 460 now block up my PCI slots so the soundcard can not be put in my system grrr)
let us know how you get on
chaz