I'd suggest you stay away from Schumacher nitro cars. The R12 and the Fusion 21's design are intents of Schumacher trying to get their electric cars turn into nitro. While they are very light and fast, their durability sucks. And I wish it was durability when it comes to crashes, its not even that. Their belts practicly shatter under the most slim stress from braking.
The Traxxxas 4-tec and the RS4 3 are very old cars. The RS4 3/2 are usually used still in drag racing for being somewhat lightweight. Both cars have atleast 5 years on them.
The R40 is an awesome car but you need a torquie engine to move all its weight.
I'd suggest you get on eBay and find a RTR or almost RTR MTX-3.
But like Artificial-I said. The key is in the engine, gearing and the pipe.
eBay user id: riketsukirai
Selling all my MTX4 parts, bodies, radio and everything!