Looks 650b?
The old one was only 26 maybe they have decided to use the 650b too which required a new design for geo and what not. If so that is pretty evident that the 650b is faster.
A lot of people are set on thinking riders are only using them because sponsors are telling them too.
Personally I think that is BS and like f1 the wc is a testing ground, riders will not use something slower.
Mick has said he looks at the clock so if they have moved to it, it may indicate be has tested it and it is indeed faster.