Comment by lynndotpy

Yes! But I do agree, six or seven units are not enough.

Extending the music analogy, we could call those powers of two "octaves", and divide it into twelve exponentially-spaced steps (i.e. 2^(years/12)).

The break even is about 75 steps (i.e. six octaves and three steps), which is about 76 years, since 2^(75/12) = 76.1.