Hi there,
What do you mean ideal numbers?
The 3, 3, volts are for digital circuits, the 5 volt circuit turns your machine on, it is also used in standby mode (the 5 volts that is) so when you switch your machine 'off' at the button it is ready to switch it back on again when you power up,
The 12 volts run your fans, drives etc.
Mostly amps & watts is what you should be concerned about.
Ben.
If you are talking single rail vs multi rail that is a different subject.