I am using the 8.25:1 gearset, 7 tooth pinion, and a Tomy 2.6 motor in my fastest car, (a shen Skyline) and I have beaten everyone I race against. (Of course I don't personally know anyone else who's gone apesh*t over modding these cars like me either!).

I've tried using the HW KIT racer gearing (same as Bit racer), but it's just never impressed me. I generally pull the wheels and use Bit gearing with the most success.
(I understand multi-battery mods tend to do better with them)