Can we speed up bootstrapping by starting circuit building earlier?

In #3196 (moved) we're heading toward slowing down bootstrapping with the hope of making the first thing the Tor user clicks on not compete with the "fetching the rest of the descriptors" phase.

If we start making circuits at the "25% of descriptors" mark, but don't call ourselves bootstrapped until both a) we have a circuit and b) we have 75%, how much time do we save?