Hi Max,
by now I flew the AQ on following copters:
QuadX, 45cm span, Hacker A20-26M, 9x4,7" props, 3S, AUW 1kg
X8, 70cm span, Smartdrones 550, 15.7" props, 4S, AUW 3.2kg
X8, 70cm span, Tiger MT3506, 13x5" props, 4S, AUW 3.3kg
Flat Octo, 100cm span, Tiger MT3506, 13x5" props, 4S, AUW 3.8kg
Flat Octo, 88cm span, Plettenberg Orbit 10, 12x5" props, 4S, AUW 4.3kg
There were some well powered copters but also underpowered copters. As you probably know a 3.8kg Octo with MT3506 is no rocket at all.
If the mixer values are too high, you need to lower PIDs and thus your reasoning of 100% power for emergency cases is obsolete. High mixer values with low PIDs give the same maximum output as low mixer values with high PIDs. Keep in mind that mot_pitch and mot_roll do not allow higher values than 300 as long as you don't change it. At +/-300 the output clips and this is something we don't want.
Instead our goal is to use the maximum dynamic of mot_pitch and mot_roll to be on the safe side under any circumstances. Your high mixer values didn't help to recover your copter more than lower mixer values with higher PIDs would do because in both cases pitch and roll is limited to +/-300.
I have read Angel's paper and it confirms my experience. If your mixer values are too low, you will lose dynamic in controlling pitch and roll. If they're too high, you will have too much dynamic and you have to reduce it by lowering PIDs. At the right point (maximum mixer values but no PID tuning necessary) you reach the point of maximum dynamic.