The frame may well be too small. It's a 19" and LBS sized me to it back in 1995 and another LBS sized me to a 20" Trek 7.2 FX in 2007, which is a very similar bike. Since the sizing changed between the two models, the LBS's were pretty consistent in sizing me. I would like to try a 21" multitrack but finding one local or nearby has been difficult.

It sounds as if there really isn't any upsides to going 650B so I guess that pretty much answers my questions.