Langebaan

Will 29er wheels fit 650b fork/triangle?

I ride in Langebaan, not much climbing. I average 21 kph over 40km offroad with elevation gain of 380m

I am an average rider and will be doing my first CTCT (Cape Town Cycle Tour). What average speed can I expect if conditions are fair? Riding a Camber Comp 2x11 29er.