Originally Posted by
FrozenK
While no, there is no scientific study to back it up, my personal experience (and that of everybody I know) is my dataset. Couple that with the fact that people regularly service and replace external BB while servicing and replacing internal BBs used to be pretty much unheard of and I think my comment is substantiated. Mind you, I should probably clarify I'm talking about threaded bottom brackets. Press fit one's are all over the place right now in terms of durability.
My own personal experience, as well as that of two buddies, one of whom races, is completely opposite of yours (with exception, as mentioned, to powerspline) in that no problems have surfaced with either external or interal BBs. That's the problem with anecdote, the sample size is 1 and often contradicted by some other bloke's experience. Ie it's useless as an extrapolated statistic.