If using the optional wheels with this stand, what is the difference (if any) of the standing height of the drum compared to the same sized drum sitting on the Cross Stand?

It depends on where you attach the wheel. Wheel's height is just 4.5cm and stand's height is 5.5-6cm. So, total height is about 10cm. Not so big difference but the height of the cross stand would be a little higher than square stand with wheels.