For cycling in hilly areas I'm referring to the torque available to assist the rider in cycling up hill in a low gear with reasonable speed, comfort and cadence.
you see and explain clearly why choosing a motor with good torque.
There is no agreed standard torque measurement for advertisements on rear hub motors as the maximum torque will increase when the speed drops until close to stalling point, it drops exponentially until it stalls, like the proverbial brick.
as I understand, the hub version uses a Shengyi motor. I use some of their models myself, DGW07 on my Camino and DGW22C (C=with cassette fitting) in hub kits. Shengyi will make motors to order, so you won't find the maximum torque on their website.
A lot of users do not know the formula connecting motor yield to RPM, battery voltage and max Amps to power and power to torque, so they don't see clearly the interaction between these elements. For a detailed understanding, you need to get down to formulae.
Starting with power:
Power = 36V (or 48V) * 17A (typical on e-bikes) * motor yield (conversion ratio output power/input power). Motor yield (0%-87%) varies with the wheel's rotational speed or RPM. The motor yield curve is shaped like a wave, best only in the middle, zero at both end.
Power to torque:
power = torque (in NM) * rotational speed (in radians/second)
So for the same power, less RPM = more torque.
Your first job is to define what is your minimal acceptable yield. Too low, most of your input power is turned into heat harming your kit. Let's say 50%, half into useful work, the other half shed as heat.
Look up the test charts that the motor manufacturers give you for the minimum RPM. For 50%, you have typically 100RPM (or 8mph on 26" tyres) for the DGW07 and 80RPM (6mph on same tyres) for the larger DGW22. So, if you have steep hills, you will need the larger DGW22.
For practical evaluation, let's say that we use a 17A controler at 48V at 50% yield.
Power = 48V * 17A * 0.5 = 408W
If you own a DGW07, your torque will be at 8mph/100RPM
T = 408W /(2*pi * 100/60 rad/s) = 39NM
If you own a DGW22:
T = 408W / (2 * pi * 80/60 rad/s) = 49NM.
Shengyi will make custom motors, but the motor dimensions stay the same so the calculations are similar. Google Shengyi motors for other characteristics.