I received another 285GTX and am looking to SLI it.
my currently setup is
intel quad9450 o/c to 3.2mhz
XFX GTX 285 x 2 hopefully
XFX 790i Ultra SLI MB
8 gigs of (4x2gigs) OCZ 800 DDR2
2 x 80 gig sata 7200 hard drives raid 0
Antec 650w truepower trio
6x case fans (1 led) 5 = 120mm 1=140mm
Coolmaster Storm Stealth Case
It is on the low end but will probably work with its 52amps on the +12 volt rail. For a single card EVGA recommends 40amps +12 volts but XFX 46amps both of them have some safety margin built in.
To be safe a move to 750 watt psu might be in order.
And inputting what info you gave, they suggest a 731W (681W min) power supply, for whatever that's worth to you. This assume SLI with the GTX 285, and your C2Q9450 @ 3.2Mhz (I estimated 1.45V on vcore)