It's pretty vauge, but if you want to use it, i strongly suggest that you visit the "Punk Town" roleplay OOC in the Arena, and the Multiverse Character Deposit in the interest checks; the latter has a bunch of tier 4 characters, skimming through them will give you a general idea of how this works.
The tier system uses speed and strength as measures - of course, those just outline the boundaries of any other sort of power. At tier 5, if you choose to focus solely on either of those parameters, leaving all other abilities of your character at an average human level, they will cap at 30 tons for strengh and Mach 1 (speed of sound, if im right) for speed; both numbers multiplied by 5 for a tier 6 character. Again, those are the highest possible values, achived only by making your character completely impotent in every other way.