I picked up a pair of 650B rims on clearance at a VO warehouse sale. It was an impulse purchase. I have several other bikes with VO rims, so the weight difference here is minimal. I have yet to spring for carbon wheels, which seems to be what you are using for comparison. Yes?

Anyway, a large snowstorm and grandkids in the house gave me reason to lace them up. (Boy, did those eyes get big when they realized grandpa was making wheels outta nuthin'!).

ALL my bikes are C&V, but those originally built for 27" wheels don't take 650B very well. Few long-reach brakes are long enough. BUT, the wheels fit very nicely into my 1971 Gitane TdF. I put 38mm Col de la Vie tires on, as it wasn't clear if the 42mm tires would fit. I have an advantage in that I have a 1971 Gitane Super Corsa for control comparison, too.

Bandera, I keep looking at that 1974 Raleigh International in your signature. What a great frame for 650B wheels. What's the big deal in lacing up a set and giving them a try? It's clearly not big bucks. At most you might have to swap in different brake calipers.

My TdF is not especially faster with the 650B wheels, but the comfort change is very distinctly noticeable. I don't think it is necessarily slower, either. Cushier, is what I'd say. I like to rotate bikes, and now generally put the TdF after a tight-framed race bike with skinny tires - just for the contrast. I love 'em both, but the 650B sure does put a big grin on my face.

I, however, hate peloton rides.

YMMV, as they say.