Forget mud clearence there isnt even tire clearence.
The 29rs just look awfull with the rear and front triangles overlapping in a downward way. The oversized wheels seem to help emphasize the frames .....crushed look.
Is it just the Americans that are into the 29r thing? Dont see any here in the UK and my Canadian friends generally just laugh at the idea of choosing to ride a bike that is actually harder to climb up a hill than a normal MTB.