It's also about how the ESC reacts when it suddenly runs out of range. I have a 27mHz AM controller and receiver as well. However my receiver wire was way too short, so I extended it so the overall length is about 20 inches. I haven't had much trouble with going out of range, and I've raced it in a big open lot of grass without much trouble.
Before with my CPR-01 (ESC and receiver in one) when it would run out of range, I'd have that problem, where it would go full throttle till I came back into range from running towards it. I was racing near a beach after I lifted my TT-01, and the thing almost took a plunge...
I just recently got a GTX, and I tested what would happen if it suddenly ran out or range. I pulled full throttle while holding the car, and shut off my controller. The ESC also went full throttle, but only for a second and pulled the brake. I believe this was programmed to do this by Novak.
But if I were you, I'd get an FM controller. I would get one, but I am looking for a 3 channel controller for a good price so I can flip up the headlights on my trueno with the 3rd channel servo