Anyway all that I've wanted to say that the best PSU is the one that gives more current for the CPU, and not to be forced to rise the voltage to achive the necessary power when under full load. More voltage means higher temperatures, and risk to damage the CPU.
Also a part of that current goes to the other devices, so the cpu still has less current and needs a rise of the cpu voltage, but is lower on a higher current PSU ...
The problem is that if there is a PSU that gives enough current it gives also more power than necessary (because of that 12V rails, example 12*90Amps=1080Watts)... That's why for better overclock is better higher power PSU.

For a normal user with a little oveclocking skills, not enthusiast overclocker, It will be good an 700-850W PSU, but to have a good +5V and +3,3 amperage and at least 40Amps on 12V single rail.