Don't overthink it. Hybrids are best. You will get best speed at 50V or closest to it. Speed max determines how much torque the motor will have at high speed. (Or even how fast a speed it will run without stalling.)
The motor that will give you most torque and speed with the G540 is the 50V Keling 570 KL23H2100-50-4B. At 3.5A its torque will detune to 399oz. Second best is the 54V Keling 381 oz KL23H2100-35-4B. (Frankly, I would use this one and save the extra money, as you really won't miss 18 oz much.) The 65V K387 comes in third with max speed somewhat slower. Loss of RPM will wipe out the 9 oz it has over the 381. The 85V K425 will run much slower, so it will actually provide LESS torque at a lower speed than 381.
You only need a 7.3A 48V PSU to run 4 3.5A motors.
Torque speed graphs are driver/PSU dependent, so cannot really be used for comparison unless using exact same components. They are often rigged to make the motor look better than it will actually perform.
CR.
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