You'll know your overtiming as the motor will stutter and won't work...
Simply put, 60° of real timing is about the limit any
motor will sustain. End of.
If anyone states their putting 80° in they are talking crap, as the motor would be going backwards...
Don't believe me? Take an old brushed motor that you can adjust timing on, and whilst running it on a few volts, rotate the endbell and see what happens when you get to 90°. The motor will start to stutter and become effectively confused as to it's position.
The same thing happens in brushless motors when running high motor timing advance coupled with high esc timing levels. The sensors will struggle to find the correct position of the rotor, making it stutter, or in the worse case, go backwards! Oh, and all that adds heat!
As most motors tend to need a bit of advance to run smoothly, (Around 20-30° for most motors, although I believe the X12's have nearer 40° built in), adding more than 30° of added timing brings them into the realms of diminishing returns... eventually to the point of just adding heat for less power.
Having said that, I haven't got into the fact that the timing naturally retards as you rev up a motor though, so adding timing does help...and why boosted profiles are more efficent than blinky. But, at the end of the day it's all a balancing act for best performance.