I have a cooler master eXtreme Power Plus 550W with a power rate of DC output +3.3v/25A, +5v/25A, +12.1/16A, +12v2/16A, -5v/0.8A, -12V/0.8A 5Vsb/2.5A. i7 920 OC 3.6Ghz gainward 285GTX OC 700Mgz.
I find that i get slow FPS in FSX about 15fps over new york city maxed out. Yet if i run 7800GTX 256meg x2 Sli im getting better FPS using 182.06 drivers vista 64 6Gb ram.
The 7800GTX cards have given me way better FPS no matter were i fly. I have run the 285 on a 2nd PSU with 1 and 2 power connectors with no change in performance