moosie,
You ALWAYS choose a twist based on the longest/heaviest bullets you plan on using. The lighter, shorter bullets will take care of themselves. You can spin a bullet faster than what's "needed" without any problem. You won't "overstabilize it" (no such thing), you'll merely have a higher Stability Factor than what's actually required to keep it nose on. Going the other way, with insufficient twist and too low an SG is likewise ALWAYS a problem.
My caution here is based on Berger's recommendations, and the fact that the scenarios they calculate their SGs on still have a few wildcards that can come up. I've mentioned before that buttoned barrels can easily (and routinely do) vary by as much as a half inch from their stated twist rate. Faster or slower, purely luck of the draw in the case of your particular barrel. I just like to have some edge for such little bugaboos . . . just in case.