Doing fairly long climbs up steeper grades with loose surface I do prefer the extra cush of a wider 650b.
For me, there's only about one tooth jump between 700c and 650b. 700c being on the larger cassette cog.

A narrow 700c with deeper knobs can match the climbing grip of the 650b with lower knobs, but it is a harsher ride.

Makes a difference also when you're running 1200gm wheels and one of the lighter 2.1/2.2 options.