First of all, Brushless is very very different from brushed motors. Usually with brushed motors when you gear lower you have more punch, less top speed, when gearing up, less punch, more topspeed.
This is not the case with Brushless...if your gear ratio is too low, you have zero punch and topspeed, same when it is too high, so its very important to find the right gear ratio.

Also, Brushless takes a lot of energy on fast open tracks, sometimes you will even have problems dumping on that kind of tracks. On small tiny technical tracks runtime is sure no issue.

I experienced that the 14mm bonded rotors are not good, simply no punch and the efficiency is bad. Daniel is right, when he says that a 14mm sintered rotor is more efficient, sure it is, and it has crazy torque. But one big disadvantage because of the strong magnet field is the braking effect off throttle. When you wanna gain runtime use that rotor with taking off all the automatic brake on your speedo.

I also tried the new LRP 12.5 and 13.0 sintered rotors. Very very good solution for 12scale. Its more driveable due to less torque and it rolls better off throttle. Ok, it has less runtime than a 14mm rotor......
With a 12.5 and 13.0 set your LRP/Nosram speedo on automatic brake program 1.

I usually run a 4.5 LRP motor...here are some good points to start with:

small tracks:
12.5 rotor = 28,00mm
13.0 rotor = 29,00mm
14.0 rotor = 30,00mm

big tracks:
12.5 rotor = 32,00mm
13.0 rotor = 33,00mm
14.0 rotos = 34,00mm

Hope this helps a little....try to find the rotor that fits to your driving style and have fun!
Markus