[BrianG]

I don't there is a definitive answer here either because there are so many variables.

If running at more or less constant high speeds, I can see the high rpms heating the motor up more. And really, smoothness is irrelevant at high speed running anyway.

If running where the speed varies a lot with little top-end speed, I can see setting up the system for higher rpm to give more control at the lower speeds.

So, there is no one-size-fits-all solution, but the 35k "golden rule" can work for all around use. I just prefer smoothness at low speeds along with high speed capability.