Anything you put in rock it will tear tires or tracks up even the bell, actually a company in STL converted there john deeres over to metal tracks for when the dirt gets rocky.
Your right the bell wont spin tires it just boggs down and stalls, i ran it didnt like it.
All john deeres and quads have a differential lock that allows all 4 tires to spin, you thinking that they didnt makes me believe you have never ran one. Deere dif lock is right under the steering coulmn quads its on your right console, 2 switches, its kinda nice on the quad cause you can lock up one side or the other.
Fuel consumption im not really sure, but im sure the Bell cannot burn that much less then the tractors.
Have you ever ran the wide tires up against the duals??? We have ran the dual setup against the floater tires and the duals do better hands down on the 9630's the floater tires do just that, and you cant get any traction.