Interesting Project Idea...

[J3110]

Sounds interesting.
If you need a better ESC, many of the battlebots guys use Vantec speed controllers:
http://www.vantec.com/rdfr.htm

I'd go for the RDFR47E: "Heavyweights, 3HP Acrobatic Go-Cart"
Worked fine for pushing 325lbs around on metal plate conveyor belt tracks:


It might be overkill, but these things most likely won't fail on you like some of the other "100a +" ESC models have been.