I don't know about those advertised speeds on the Traxxas trucks. I mean, they will go that fast, but the engine probably won't last more than two gallons of fuel being tuned for that kind of speed.

I don't know if you've ever actually clocked a big truck doing a real 45mph, but that is FAST. You kind of have to push a 4S system to get 45mph in a truggy and things will start to heat up. You can do it more easily with a 5S system, but I think it's still too fast, even for bashing. I'd be more worried about gearing for good running temps so that you don't have anything to worry about while you're having fun. Then, if the occassion should arise, where you need more speed, then you can just do a quick gear change.