savage21 brushless conversion

[notatoy]

hi guys need your help yet again ,, converting this nitro savage 21 to brushless have most things sorted thanks to this forum confused on gearing i have the stock two speed transmission lockd in second gear . with a 47 tooth spur gear mod1 , also have a mod1 13 tooth pinion . not sure if this is correct ???????? need your input will be running 4s and 6 s best gearing options plz guys .. some have said go to a 17 tooth pinion ??? small pic of this savage thanks .