What size gearing would you recommend.

Hi, I am planing to go with a Tekin 1700kv motor/combo on 5s in a Truggy.
The Spur gear is a 50T.

The clutch bell that it was running with nitro was a 13T.

The question is what would size would you recommend for a pinion gear for this motor battery setup for racing.

Should i stay with a 13T or go up a few sizes or down?
Any information is greatly appreciated.
Cheers.