[apalrd]

Why do you want a really low low gear? What objectives does it achieve?

Why do you want a really high high gear? What objectives does it achieve?

I don't really care if you optimize the benefit of adding the extra motors, the goal should be to optimize the system as a whole.

There are a lot of variables that you aren't likely seeing. Not limited to electrical system resistance, battery current capacity, motor heating/thermal performance, and the acceleration/current profiles which are all important differences between 4 and 6 motor drives. I can't say for certain how important they are, since I don't have data proving most of it one way or another, but I have lots of subjective and theoretical suggestions.

I am well aware that 6 motors is a marginal performance gain theoretically. The limiting factor moves from the motors to other things somewhere between 4 and 6 CIMs, which is why you don't see much improvement.