i'm from the school of thought where rotating mass is an important factor..
larger spurs/pinions have a higher rotating mass, making them slower to start rotating or stop rotating..
the opposite would also hold true, small spur/pinion has a smaller rotating mass, making it easier to start/stop rotating
so to my way of thinking, if a small spur/small pinion combination achieved the same ratio as a large spur/large pinion combination, then the one with the smaller rotating mass will be able to accellarate quicker and stop faster (and run cooler as the motor doesnt work as hard)..