Around 5 minutes in your video. The room helpfully marked by a stairs picture over the entrance. I assumed it was a brig because of the Covenant coming out of locked rooms, but in hindsight that seems dumb.

: I know the feeling of course. Your shield can go down in a flash on
: Legendary. Is pistol & AR your favoured combo, or were you just using
: it to compare with my run?

I did it for comparison. My fastest full speed run was around 6:30 on PoA, using plasma weapons and the assault rifle, and at that time it was still 30 seconds slower than the fast run. I probably wouldn't be able to beat your plasma gun kill em all run even if I tried really hard.