I think you have answered your own question. You could live with 4.10 (lots cant), and like the idea of 3.91. So, go with 3.91!
I used a roadrunner with factory 4.10s as a daily driver, work commute car for years, and it was tolerable because of a quiet factory exhaust. Most that dont like that much gear, dont like it because of too much noise.
I have 3.91 on a locker in my bracket/street car, cause it was just as quick as with the 4.10 and 4.56 that i used to have in it.
I have 3.50s in a nine in my other car, for potential nitrous use, to avoid running out of rpm at the track. If a car picks up 10 mph or more from nitrous, (very easy to do),too much gear can be really bad.
