MBX-5 going BL. Center diff question.

[SilentMonster]

Well I think I have decided on the MM ESC. Should be here Monday. I don't want to take the chance with 5S. Gonna run 4S but may drop down from the 10AH batteries to the 8AH. I just want to be able to run a 20 min. main and after seeing glassdoctor's run last week That shouldn't be a problem. I've got several 4800 Orion/Kokam packs. Thought Id test run with those to see what it's gonna take for sure. So now on to the motor. I keep going back and forth on whether to run the Neu 1515/2.5d. and hope for the best while waiting on the update from Castle or just go with the Lehner 1940/9. But whats up with that shaft size? Also I don't seem to understand what the difference is in the Hi amp version. Any and all thoughts and criticism is more than welcome. Is there a better motor choice? I'm not looking for stupid fast. I've done all my calculations based on 40mph. My two main goals are: #1 to be more than competitive. #2 efficient. Later, Stephen