Use 64p schuey gears,
For 5cell on a small sized track = 114 spur + 22 pinion
For 5cell on a medium sized track = 114 spur + 25 pinion
For 5cell on a large sized track = 114 spur + 26 pinion
For 6cell on a medium sized track = 118 spur + 20 pinion
Try different rotors in the 3.5.
and timing is also very important, and all brushless motors are different and you have to find the 'sweet' spot.
Twisting the end of the motor Clockwise = more acceleration + more runtime
Twisting the motor Anti-clockwise = More top end speed + less runtime.