I popped your configuration into the speed calculator and it says 35mph. If your vehicle really does go 40 with that setup, then my 9XL on 4s should be doing lower 40s with a 17/36 gearing and slightly larger tires.
The timmy - Revo 3.3 MM 9XL 4s , Rustler MM 4600 3s
The ferty - Dual velineon Revo 3s, Rustler velineon 3s