From my research, it is a boost leak, confirming my initial observations.
My main issue is finding the damn leak. I'll have to do this in the new year.
I edited the video to remove a lot of filler, so I skipped to important bits. I held it in the ideal RPM of 1500-3000 and first gear for best results, and shifted at a higher RPM than usual as well.
I get both a wooshy noise on a medium-hard acceleration and lifting off only after the turbo has spooled up, and a high pitch whistle intermittently at about 1.5K - 3K RPM, and only stops when I start accelerating again.
You can hear a woosh at about 2:25, and an exaggerated whistle at 3:00, and hearing another little woosh at 3:25 with the whistle again afterwards. I have heard both at once as well.