Top speed race class

[Serum]

Would be fine;

They updated the diffs as well; still two planetary gears with two satelites, but they upgraded it with an extra steel insert. (tunable with silicone-oil) they also increased the chassis length, and lowered the entire CG of the batteries a bit.

here, the exploded with the diffs;
http://www.traxxas.com/PDF-Library/3905_rear.pdf