I have three sets of 650B wheels. The best ones were an eBay find: Rigida Sphynx rims and Campy Record hubs. Far down in the hierarchy are a set I built with Weinmann Zac-19 rims and Dura Ace 32-hole hubs. The most frustrating are a cheapo set of Sun CR-18 rims and Shimano Nexave hubs. Those Sun rims were slightly oversized, so mounting a tire is quite a struggle.

Neal