I'll give the long wire brush a try (though I'm going to have to improvise) and see how well I can clean it up. Hopefully it will also give me a better idea of whether the bb shell is affected. If I'm not entirely happy, I'll take it back to the shop that built the bike for me since it's one of their own frames, even though it's been a few years now. The location of the rust spot does worry me.

Thanks for taking the time to help me out.