According to Gates Rubber, the main cause for cog belts to break is due to the belt climbing up on the pulley grooves. That can happen if the rear fork gets pulled forward due to worn bushings or the belt is too loose to start with.
Anything that would cause the distance between the wheel pulley and transmission output hub to decrease, would increase belt slack and cause the belt to climb on the pulley cogs.
I seriously doubt the belt is breaking because of excessive Torque. The Boss Hoss 502 use a belt system also. Yes, a bigger belt but it's not 5 times bigger.
But if chain is what you want, do it. It will hide the root cause for the belts breaking.