the taller the tire, taller the blades, or the more blades there are, the harder it is for the engine to turn them over. A mostly stock blaster geared 13/40 would work well with 20" 8 blades (ITP sand stars for instance) for all but the steepest dunes.
If you upgraded the induction system, pipe, and got some porting in that engine to help it breath better you could probably pull the same paddles with 14/40 gearing and reduce the amount of shifting and bogging.