Q: Or will I have to settle for a 8600GT OC edition?
A: The PSU brand/quallity matters most, but even a cheap power supply can run an 8600GTS. The GTS uses the following amounts of power: Idle > 21W - 31W - 47W < Max load Devide 47 Watts by 12 Volts and you only get about 4 Amps. 19 Amps is enough to actually run three of those cards. :P