studysession,
that's installed in their Heng Long "Mad Truck." The electrics is by modellfun.com

[link=http://modellfun.com/b2b/products/blmonster.php]http://modellfun.com/b2b/products/blmonster.php[/link]

Here is a simulation data curve for a mabuchi 540sh motor:

[link=http://www.mabuchi-motor.co.jp/cgi-bin/catalog/e_catalog.cgi?CAT_ID=rs_540rhsh]sim[/link]

*Click on the blue links to the right of the motor designations.

Under no load, when voltage doubles, the current draw doesn't go up that much at all.
What makes current go up is frictional or torque force required to move an object with weight from rest. Friction is like a constant torque force always fighting your direction of mobility.

You can obtain the frictional losses of your R/C buy measuring your amp draw with your motor on nothing and then measuring it with your motor installed and the wheels off the ground. The current draw will go up and then settle, but will be higher of course than with the motor running free.
Since the voltage is constant (by your control) and the motor is the same, you can use this technique.

I did a test with a brushed motor coupled to a mod motor. It didnt matter at what voltage; when I took off the brushes on the mod motor, the current into the motor being powered dropped around %27-30.