can currently do 35mph and don't want to give that up for a little efficiency...
This make no sense to me.
35mph you pedal at 116.5rpm...i'd like to see that
ATM your drive has much less than 2000W, so what I calced for you must be huge increase.
To make things clear:
The crank to MACshaft drive ratio sets the efficiency
at normal crank cadence
The theoretic max speed
is set by the MACs output gear
The burst power
is set by bat_voltage*_max_amps*efficiency
The continuous power
is set by efficiency in most used Q-point, eg. @80rpm cadence, cause it defines the rejected heat
if max heat rejection of a MAC is let's say 400W unmodified. So @ 80% efficiency a MAC can do max 1600Watt continuous if driven in it's best efficiency point
you see, these things are completely independent. The 39kph i mentioned are a "virtual" number to calculate with (to make it possible using the data from ebikes.ca in a middrive setup). read my calc carefully, i'm certain you'll get it in the end.