I did a b+ versus 29″ test at my local xc loop. Same bike, different wheels. Similar style of tyres (front more aggressive). I did 5 Laps on each, with target heart rates. This was on two different Sundays with a similar build up in the week. The 29″ had the disadvantage that the conditions had deteriorated a lot.
I swore the b+ was faster. My wallet wanted it to be faster, I’m sure I tried a bit harder on it too.
It wasn’t as quick as my 29″.on the fast laps.
What I did find interesting was that on the lower heart rate Laps at the end, the b+ was showing it was a good margin quicker….
Maybe when half arsed riding it’s quicker, but not flat out.