Hi Guys A couple months ago I built this system:
AMD Athlon II x3 445 [Unlocked to Phenom II x4 B45, overclocked to 3.7GHz by increasing to about 240 x15.5]
Radeon HD 5770, not overclocked
Asus M4A79XTD Evo. Supports Crossfire at x8/x8.
Kingston 4GB [2x2GB] DDR3-1333 RAM
Samsung Spinpoint F3 500GB
Zalman CNPS9700NT Cooler
Corsair VX-550W PSU
I built it as such so that I could add a second 5770 in the future... but I think I should've gotten a different PSU e.g. Antec EA-650W or something for crossfire.
Do I have enough power to add in a second 5770? The eXtreme Power Supply Calculator recommends a PSU of at least 440W to me, but that sounds awfully low, even though the 5xxx series are pretty good regarding power usage.
And for reference, yes I would be willing to undo the CPU overclock or even just re-lock the 4th core and L3 cache if it would help me.
5770s are very light on Wattage. Each one has a TDP of only 160W (Maximum) so to Xfire that'd be 320W leaving 230W for the rest of the system. I believe the chip only uses either 65W or 95W, so that still leaves at least 125W. And since it's a Corsair PSU, it will reliable give you all 550W
So to answer your question, go head and Crossfire!