I run 69er on my Monocog. I've been comparing it to 26er for awhile now, switching between the two. I honestly like the 69er setup the most, even though the geometry isn't specific to a 29er wheel in the front. It is good at slower twisty stuff, and also faster on downhill sections. Overall it seems to be faster than both the full 29ers I've tested, and 26ers. Don't really know why this is so, but me and the local shop monkey have settled on the 69er setup.