Since Mike basically guessed this one, it seems like a good thing to spill for today.
The Supers20 Power levels (which are guidelines not rules set in stone) are:
Gritty (Beginning Level 1, Beginning Max Power Level 1, Max Power Level 5)
Street Level (Beginning Level 5, Beginning Max Power Level 5, Max Power Level 10)
Four Color (Beginning Level 10, Beginning Max Power Level 10, Max Power Level 20)
Cosmic (Beginning Level 15, Beginning Max Power Level 15, Max Power Level 20)
I'm still wrestling with the idea of going beyond level 20 for Cosmic campaigns. It makes sense, which isn't to be confused with me wanting to deal with it.
Still, I probably will in the end, since I tend to think of Superman as being at least about level 25.