Why is your main goal tire spin? If you're spinning tires in higher gears you have way more power than you need and that's just going to create a tedious auto-x experience. I'd rather be able to point the car, mat the throttle and go rather than fussing around with modulating throttle to keep the car from pushing everywhere. I think you need to pick your focus. Setting up this car as BOTH an auto-x and drag car with lofty expectations for both is going to be frustrating.