There is a "life expectancy versus strength" scale associated to the levels. That's an universal scale, it's used for all female channelers (For AS the effects of the Binder are calculated afterward).

That scale is purely linear, the same fixed number of years is added to life expectancy at each strength level, from the lowest level to the top. The same difference in L.E. between Lanfear and a level 2 woman is found between a level 66 and level 65 women. It's the same at the median level as well.

That certainly suggests a purely linear progression across the levels for strength as well.