What's the difference between... say... a Les Paul with mini-humbuckers and a Les Paul with real humbuckers?

Do the mini ones sound...

- Weaker?
- Quieter?
- More trebly?
- More... or less... something? :confused:

What's the difference?

And how do they stack up to single coils?

Also, P-90s... what do those sound like? How do they stack up against humbuckers and mini-humbuckers? Against single coil?