Here are the two bikes I ride most of the time these days (for fun, not for commuting)
I posted about the Look recently here
As a pair they’re a reasonable example of what this 650b thing is all about, but they’re very different bikes in other ways. I’ve ridden them both on the same loops a few times now and although they feel very different with totally different SensationsTM, there’s not a lot in them speed wise. The Look has surprised me with its comfort on paved roads over <4hrs too.
But 650b opens up all sorts of rougher surfaces, and over longer distances. I’d much rather be on it for a whole day or more (I think. I haven’t ridden the Look that far to be fair).
This isn’t a thorough analysis with a strong answer. Just my thoughts
Incidentally, I replaced the 700c x 32mm wheel on the back of my commuter with a 650b x 55mm and it’s very comfy.