Several years ago our American Legion Post participated in the committal service for a WW-II P-48 Fighter Pilot whose remains had been recovered in Germany and later identified.
At the service were several WW-II Veterans, including one who used to be a P-48 Jockey until he transferred to P-51s.
I remember him telling me later at the reception that the P-51 was the first fighter that could pull enough Gs in a turn to black the pilot out, and it was a significant problem until they developed pressure suits to counteract the effect of the G-forces. It was also so fast that it was extremely difficult to bail out of. Not long after the war, they got to work on the ejection seat.
AFAIK they probably started research on it while the P-51 was still in service.
Apparently they lost a fair number of pilots to these emerging phenomenon.
The Mustang was popular and sexy, but it was apparently not considered to be a particularly safe airplane to fly.
I wonder if the pilot pulled enough Gs coming around that turn to black him out? At those speeds and altitude, even a momentary lapse of consciousness would be (and may have been) fatal.
From the video clip it appeared as if he came in at about an 80 degree angle at around 300mph (rough guesstimate).
If it was a blackout, he never woke up in this World.
From pictures, I believe it was a highly modified razorback P-51 -- even harder to get out of than the P-51Ds and later, with their bubble canopy...