The super rooster is unlimted especially on one motor, this was made for twin motor set up. the others , lrp runner traxxas and the futaba are basic speedies and will blow easy with a mod more than 19t . Yes you can run a mod with lower turns but they draw way more amps and will kill the basic speedie. Add to this if you over gear the vehicle your motor will draw even more amps.
You are better of getting a second hand race speedie than buying a new budget one as they can handle almost anything you put on it. Hope this helps.