rc10 mod

[rc-10]

So I have been wanting the old school rc10 B2. But I'm bring the new tech on board and don't know what gears to choose?
I bought the speed passion 10.5T with a 120 amp ESC and a 5000 mahsaddle battery
I like the rocket sprocket 84T spur gear. But not sure what pinion gear to use?
So I bought a kit with assorted flavors 19- 24.
So my question is which pinion gear would be best?
I want this to be a competition racer and a speed passion! LoL
So please feel free to give any info on what you guys think I should do