For example, from the Sanyo Denki StepSyn catalog (NEMA 34):
motor 1) #103H8223-0441 887oz-in, 11.2v, 2.0A, 5.6R, 24mH
motor 2) #103H8223-0941 887oz-in, 5.4v, 4.0A, 1.35R, 5.6mH
The only thing that comes to mind is that the motor with the lower resitance/higher current might reach it's rated torque quicker each step. This may allow for greater acceleration. What other differences would these two motors exhibit if not that?