Another question about Feigao motors

I've been going back and forth trying to decide which Neu motor to get. I want a Neu for no reason other than the efficiency, or more specifically, cooler running.

My appreciation of what goes on that causes heat is that the heat is caused by the current flowing though the motor. Higher wind motors have more resistance, so they flow less current and run cooler, given a fixed power source. The Feigao, being as inefficient as it is, converts less of the current to power and wastes more as heat than a "good" motor.

When running a 7XL on 4S, it got hot. Really hot. I moved to an 8XL and it got hot too, but not as hot as the 7XL. I tried out a 9XL and that ran even cooler. I'm planning on running a 5S setup, with my sights on 6S when an adequate controller is available.

My question is this...how high a wind do I need to go to before I hit the point where the motor does not generate more heat than the motor case and heatsink can dissipate? I'd like to keep temps in the 150 range.

I realize that there are a lot of variables involved, but I was hoping that some of you could share your real world experiences. I do want to get a Neu, but I'm not going to put a Neu in every vehicle that I have. My wife would shoot me, or stone me to death with all of my motors.