medusa and losi 8

i think this will be my set up,losi 8 buggy-medusa 36-60-2000 or 70mm,cant decide yet? mamba max v1 already have.4s 14.8 4000mah battery,so what do you guys think,do i get the 60mm or 70mm,lots of guys say 70mm.but what will be the best one .i want to race the buggy on my local track.and what is the best grearing for raceing.i already have 10t 12t 14t 15t 16t pinions.any help would great.