XRAY - Model racing cars

I just assembled my new T3 and want to practice at nearby abandoned playground before the racing season starts in Aug (I'm going to set up a practice track with small orange cones).

I have a Tekin RSPro/21.5 setup and I'm using the stock 84T/48P spur gear. I want a pinion that won't wear out my ESC/motor while giving me decent performance to prepare me for racing (the class I'll be starting in will run 21.5, by the way).

1) What pinion would you recommend running with the 84T spur?

2) What Spur + Pinion combo would you recommend I run for optimal performance with a 21.5 motor (assuming no guidelines from a local track)?

Thanks!