Depends on power of each motor.

Normaly I would say that a 4QD NCC70 24V easely can handle 8 speed 720s 2 in serie 4 parallel.

But if you try to control 2 Bosch 750s on the same 4QD , youll lose a lot of potential power delivered by these motors. If the speedo doesnt fry.

In theory, a group of motors looks like 1 big motor to the speedo. But if the back EMF and total power drawn exceeds the capacity of the speedo, youll be letting out the magic smoke.