My electric Class 2 is so fast and heavy that it is a real challenge for me to fly it. In the old days I would fly that speed but with an airplane that weighed half as much. This is just too much for me at my advanced age and decrepitude. So I am considering putting in a smaller motor and battery. The heavy airplane (4 lb 7 oz) seems to be just too heavy for a good low speed.
I do have a large (and heavy) motor which is the reason it goes so fast. I am hoping a lighter setup will go slower but achieve a better score due to a better low speed. I have a high cell count (10s) but that is not to get higher speed. The power our of a system does not depend on the voltage selected as long as the KV is set for the same rpm with whatever battery is being used. This is because the windings for low KV won't take the high current of a higher KV motor. It all gas to do with the fact that the internal cross section for copper wire in the same motor sizable is the same. Winding more turns of fine wire or fewer turns of heavier wire will end up with the same power capabilities. The reason to go to higher cell count, higher voltage and proportionally lower current is to save weight and money for the electronic speed controller. High current controllers are bigger, heavier, and require heavier wires than low current ESCs. So it is a budget and weight consideration, not a motor power consideration, that might cause one to select a high cell count.
Pete