I played a ton of Perfect Dark (on N64, mind) but I can confirm that damage tanking in Perfect Dark can be extremely dicey on Secret or Perfect Agent (this was Secret Agent, right?) Notably, enemies are capable of headshots in the random hit distribution, which deals oodles of extra damage, and explosions in general, depending on how they want to cooperate, are capable of ending your whole damn career.
To respond to each bullet point:
Out-of-bounding Datadyne Infiltration is a speedrunning rite of passage.
Yes, the framerate is better, and the explosions not quite as eyebleedy. The runner also discussed how there isn't a radial menu for weapon quickswitches, either, which put in some work. Also not explained, if you weren't paying attention to it, was that *every* weapon in the game that's capable of killing someone has an "alternate fire" of sorts. Some are bog-standard - Joanna's typical Falcon pistol(s) have Pistol Whip by default. Some are fun, like the SuperDragon, which turns sideways to become a grenade launcher. It was a huge appeal of the game, especially in multiplayer providing your friends aren't dicks who made your game run in blur-motion with Tranquilizers. Lastly, the "Combat Boost" that was used during the Carrington Institute invasion mission slowed *everything* down in N64, including your own movement. 360's remaster just slows down enemies.
Jonathan is a dick who ends so, so many runs of Area 51 because he has to John Woo his way into a thrown grenade.
Do not give Elvis a gun.
Yes.
I forget the context of this bridge clip - was it in the last normal level?