Problem solved! At 300 bpm at 4/4 time, the inflection is on the first beat of each bar of 4 shorter clicks. The true speed is therefor not 12 notes per beat, that IS impossible, it is 12 notes per second. I just set the motronome to 60 bpm and played the same run a few times. I actually got it to 16 for one full bar after a minute or so. That explains everything, its just the maths of it, there is no way anyone can play 16 notes between each blip on 300. Try it again set at 60 and just count the number of notes between each beat, that's the most simple way. I did a little reading and discovered that Michale Angelo has achieved 22 nps, now that's impressive!

Still though it's an interesting way of increasing speed.