Asus has a power calculator for some of it's boards, listed under "utilities". It will give you a starting point for picking a ps. I always try to use a good brand, such as antec, seasonic, or corsair. There are several sli certified ps with the connectors you need for 2 or more video cards. Don't go just by the wattage. Cheap brands weigh less and don't give accurate information about performance under load. I've seen lightweight ps (2 or 2.5 lbs) die before my eyes in just days with moderate overclocking. Some go up in smoke. Better to get a good brand rated less in wattage than the cheap brands.
Yes. Plenty. It has 70 amps on the 12v rail, higher than 90% of the power supplies out there. And the price is great, plus the fan is 140mm. I use the same size fan in my ocz, and it's extremely quiet.
Well my 1st recommendation would be the Antec CP-850. Nothing passes it in performance according to jonnyguru and silentpcreview but unless ya got an Antec 1200, P183, P193 or DF series case, it's not gonna fit.
Here's alist I compiled about 8 months ago ....For comparison purposes , the list below contains performance ratings (10 scale) at jonnyguru.com / prices as per newegg on 02/21/2010 and ones w/ double asterisks (**) made it onto silentpcreview.com's Editor's Choice List meaning they excelled at both electronic and acoustic performance:
well my point is...is 850 enough for 2x 470s and a 9800GTX in physx?
yes it should work fine unless you wanna clock the copper out of the pcb,max pull per 470 is 220watts so say 440watts for the cards just a big estimate since sli cuts power usage a bit, so 850-440=410 maybe~60 watts for the 9800gtx doing physx leaves you enough to run everything else