As far as speed goes, this thread is interesting:
I think it’s a function of the rider more than anything else. I cruise along at about 7 or 8 miles per hour. Not exactly blazing speed, but it gets me there. I tend to go pretty much the same speed on the 36 and my 32 (I don’t have a 29r, but I think it’s similar to the 32). Shifting into overdrive on the 32 definitely will go faster, but it also requires more effort. So there’s no free lunch, when it comes to speed.
Looking at the stats from the recent Unicon is pretty amazing. Scott Wilton went 26+ miles at just a hair under 20 mph average, clipped in on a G36. Wow, pretty impressive! The other stats are just as impressive, as are the videos that have been posted. There are some fast riders in the uni world!