do you know how much force your bike needs at various speeds? An interesting thing to consider is how fast it can go on 11.5kw as that is the continuous rating of the motor (regardless of the voltage applied). Can be determined by a bathroom scale weighing wheels and rider, and high and low speed coastdown tests.
This page lists 315lb/in at 2800rpm, 200 amps continuous (72v system). 72 volts can create about 26kwh @450 amps which is close to the peak rating anyway...
Mars ET-S Permenant Magnet Motor
before you buy more stuff, like %33 more batteries than you need...
So once you know your max continuous speed for 11.5kwh, you can choose appropriate gearing to hit 2800 motor rpm, and hope you have enough torque at max kwh to get you there satisfactorily (or do more maths, F=MA, or A=F/M plus resistance fudge).