b4 gearing questions

[Zoea]

Hi
I have 24 and 27 tooth pinions (and a 21 I think). I also have 84 and 78 spur gears. Im happy to buy some new pinions and spurs but first, what gearing would you recommend for :

1) EZRun 9T Brushless combo (the 380 in a 540 one)
2) 3500KV Tacon brushless with 100A esc

Also what turns is 2 equivalent to? I might get a higher KV full size motor as well.

Thanks for the help!