I bought 36t spur and 17t pinion for my 9xl on 4s, it should go 38mph. But I haven't run it yet because Castle stole my ESC. Hasn't been run in 7 months, except for a few tests with the CMS-4600 48mm motor.
The timmy - Revo 3.3 MM 9XL 4s , Rustler MM 4600 3s
The ferty - Dual velineon Revo 3s, Rustler velineon 3s