Gearing is a happy medium mate, there is an optimum ratio.
Dropping a tooth or ten in your case will only let the motor run cooler if its over geared, think of it as riding a bike, would you like to pedal along in 1st, with your legs going like hell but going no where fast. Thats what your motor was doing.
And i think changing a shaft is pretty easy, certainly no harder than changing a belt?
