[Kromm]

I'd aim for swaths that come as close as possible to 20% steps in probability of success, mirror the progression at -10 (the harshest recommended TDM on p. B346) for masterful end cases, and smooth over the discontinuity where they meet. I'd then associate these bands with the usual descriptors for power levels (p. B487) -- and note that I'm not associating skill levels with the power levels themselves, I'm just borrowing a familiar set of adjectives. Try:

7 or less

Unskilled (default users)

8-9

Feeble (beginners, humorous bumblers)

10-11

Average (most non-job skills for ordinary folks)

12-13

Competent (most job skills for ordinary folks)

14-16

Exceptional (the most seasoned of ordinary folks)

17-19

Heroic (extraordinary world-class experts)

20-21

Larger-than-Life (top experts from all of history)

22-23

Legendary ("typical" mythic figures)

24-26

Superhuman (outstanding mythic figures)

27 or more

Godlike (greatest mythic figures, gods, etc.)