Overdriven,

I use this one

http://www.scriptasylum.com/rc_speed/_gear_calc.html

and here the top speed estimator:



The upper is the standard E-Maxx andtop speed is 34mph, torque 10
The lower has a top speed 26mph, torque 13
changes in the second: from 37/13 to 43/13 and from 17T to 15T.

Don´t know from which experience you took your advice, but this says it´s different...