I have a Mayhem Pro kit without motor and electronics. I really like it.
Here is my advice on the RTR as opposed to the kit without the engine.
RTR:
Good starter package, need to upgrade steering servo.
Simply remove both servos, and put the one that you used for the steering, for your throttle and brake. Purchase a higher torque like a $50 645MG from high tech.
Go ahead and reglue the stock wheels and tires, they will come off.
And ditch the stock clutch shoes and springs. Try a better set of clutch shoes, like the white ones that are used for the MBX-5, and 1.1 clutch springs. The reason why is during the first heat this past Saturday, the stock clutch and springs didn't make it through the first heat race.
Pro:
Also, the front and rear shock towers are half the thickness than those on the pro kit. The tie-rods for the the front and rear are thicker as well on the pro kit. And anything that protects the front and rear differentials are somewhat thicker on the pro kit as well.
Thanks.