It seems like Watt Wagon's Archon X-1 upgrade to the Bafang gives as natural and efficient a power application as possible. Strapping that motor on a carbon frame with a 21 Ah battery might get you 100 miles with PAS-1. I'm reading accounts of people besting 65+ miles on PAS-2 with heavy rigs. I think the system weighs around 12-15 pounds, so that would mean you need a carbon or aluminum, or Reynolds steel ultralight frame, to strap it to (under 25 lb.)..
Please read about the Archon X1 controller here. Limited set of motors available June 2020, subject to manufacturer production capabilities. We are expecting to ramp up our production and will offer an unparalleled motor you can simply swap out. You can pick from one of the 3 options. All...
wattwagons.com
This is the best motor you can buy right now (to my understanding) to get high level PAS refinement without buying a whole platform. The torque is high on this motor, but all other things being equal, that will help you with range in the end. Unless we are talking winding or pole differences, increased winding diameter increases the efficiency of a motor, as well as inertia of the stator. Every gear in a transmission results in power loss. If you have high torque at the spindle, you'll have to use fewer amp hours of current flow to achieve similar torque assists for uphills and wind resistance. This is assuming you have a good controller, and low bearing friction. My $0.02..