I personally think that putting anything with more power than the trx 2.5r on a rusty is a waste of power. If I were moving away from the trx's for my rusty I would look at a .12 rather than a bigger mill. When you add all of that power to a rusty all you do is make it harder to control. I put my O.S. .18 TM in my rusty for a bit with the stock gearing and it was almost uncontrollable. It took a great deal of restarint to keep it from unloading the rear end every time I tried to accelerate.