In reply to Gra B:
> So...650b this, 29er that...but would anybody now buy a 26" MTB?
Yes, on the principal that I've been riding them for the last 20 years and had quite a bit of fun in that time. Larger wheels are great, 29" is here to stay (especially for XC) and I think 650 will eventually take over from 26" for DH and enduro. But 26" is still perfectly fine.
> Would the performance of a 650b over a 26" change dependant on the size of the rider?
Yes, marginally. A small rider with a small frame will find the smaller wheels easier to manouvre. There isn't *that* much difference between 26" and 650b though.
> How Would the performance of A small framed bike on 26" wheels differ to that of a large framed bike on 650b? Would it be the same?
No, they are at opposing ends of the scale, I'm not sure why you would think they would be the same. A small frame with 26" wheels will be nippier, easier to flick and turn, and marginally faster to accelerate. A large frame with 650 wheels will roll better when up to speed, and potentially be a bit comfier.