Consider the differences in mechanics of vis study though.
4 th let you study from 1-3 pawns,for a gain of stress die x 1-3. So a really high roll could be multiplied by 3.
5 th only has 1 stress die plus adds, the probability of more than a 3 level gain - at high levels - is low. I don't mind than the powers levels can be proceeded through fast. A good primer of level 5 Q 15 makes sense, so vis study should also allow his. But for book study you reach natural limits of both Lvel and Quality. Vis study has no theoretical limit, but then again in only happens very rarely that extreme rolls create extreme gains.