Well a brand name like Corsair would be good, probably around the 850 to 1000 watt range. I think you may end up putting an unecessary strain on your system trying to clock it to 4 GHZ. A threat to warranty and stability for no discernable increase in performance is the likely outcome.
I think the GTX460 is a 175ish W part. So two together will be around 350W. Lets say another 150W for your OC'd CPU and your at 500W. Another 50W or so for the mobo and other stuff, and a quality 600-650W will be fine. The biggest thing you need to make sure of is that you have enough PCIe plugs for two GTs460s. I personally would look at getting a 750W for plenty of headroom, and four 6 or 8pin plugs.
probably vendor support VGA :
if use DigitallAliance min remonded 450W
with 2-way SLI we noticed power consumption for the GTX 460 peaked to roughly 435 Watts, that's not bad really as that is slightly higher than one GTX 480 yet we certainly are more powerful.
i like corsair Vx550 good !