Do you pay attention to the air? Good air vs bad air will make a difference in power/stall speed/MPH, etc.

Overlap would have to be excessive to affect MPH, depending on how close to the stripe the shift point is.

Flare vs overlap is hard to track without data. Even a Go-Pro that you can listen to will help. A clean shift at RPM will show a fair amount of overlap when running through the gears on jackstands. I didn't want to fiddle with parts used or adjustments. I preferred to adjust the spring load in the servo to adjust the timing. There are different was to do that.

The fast, high end, performance based applications I've paid attention to often have a barely perceptible flare on the shift, I presume by design to stay away from a momentum slowing overlap.