Well, I'm not a Jammin expert, but the CR is the kit not the RTR

the X1 RTR comes ready to go, but like many RTRs it doesn't come with a race legal motor,
You may be able to race it with the .26, that up to the tracks race director, for most club races, nobody cares (unless you win LOL)

Truthfully if you get a RTR you'll want to upgrade the steering servo and battery right away at least, if not the whole radio system.

The Jammin is a good start, but I would expect to spend a few more hundies getting yourself truely "ready to race"