The speed control can handle up to 6S lipo but you can't run the 9000kv motor on 6S. The 9000kv sensorless motor can run 2S lipo.
Motor wise the 9000 Castle motor is sensorless and I think the Novak is sensored. Generally sensorless motors produce more torque and overall power because of the way the motor is wound vs the way a sensored motor is wound.
The MMP speedo is nice because it is capable of running sensorless motors and sensored motors. Castle unlike most other companies has some of the best running sensorless programming out. They been working on sensorless from day one and it runs great. The been doing sensored for only about 2 years and hit it right from the start with one of the most versatile speedos on the market and cheapest.
The built in BEC is capable of being changed to run from 5.0v and can be turned up to 7v. I normally run mine a 6v but I run 10th scale. If your running a 1/8th buggy with some of those new super high power servos that can run on 7.2 volts and higher I would use Castle BEC instead of the one that is built in. The BEC that Castle makes vs the one that is built in the MMP from Castle isn't as strong. If you run standard digital servos you should need to worry about an external BEC.
Castle Creations (Since 2005)
Bumps & Jumps RC (One of the best racing facilities around)
ST Racing Concepts (STRC) Great aluminum upgrades for many brands.
Custom Works (Best Oval Cars around). Too many titles to list
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