Gear ratio and final drive are dependent on track size and layout. The best advice would be to find out what the faster guys are running. Speedo settings will make a huge difference as well. As far as 64 v. 48. 64 pitch will allow you to make finer adjustments in your gear ratio on a single spur. One tooth is alot bigger adjustment with 48p than it is with 64p.
Team EAM // Gravity RC