Lots of positive feedback about the car here

I'm starting out from scratch in 10th off road again with the RB6 after roughly a 9 year break. I'm looking at the setup sheets and the gear ratios some of you guys are running seem to vary wildly. Starting with a 6.5T speed passion motor, what range of pinions do I need to buy for indoor carpet tracks? The gearing guide on the motor manual suggests 9.2-10:1 which would equate to around 20-22t with a 78t spur (Is the stock spur 78t?)
I know gear ratios are very specific to motor and track, but any advice would be appreciated as I don't want to cook my electrics first time out!