GTX 285 SLI on antec Truepower Trio 650w

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.

You should be good to go, considering it's a quality PSU. As rolli59 stated, it certainly cannot hurt to get a better PSU, but I think you'll be okay without.

Using this PSU Calculator:
http://extreme.outervision.com/PSUEngine

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)