I'm doing the Defense of Bruma part of the MQ and have horrible FPS, stuttering and unstability during it which makes it far from fun to do in the first place, but trying to keep Martin alive is almost impossible because of the performance (if I aim a spell at him it might as well hit a Dremora etc.). Anyway, is it safe to use set essential on Martin via the console during this part or might it mess something up?

EDIT: Nevermind, it worked out on the third reload. That was "fun"...

Not that it matters any more, but I always found that my best strategy for keeping Martin alive was to ignore him, and attack any Daedra that were likely to cause him problems (which ones depends on level) as soon as they came out of the gates. Then leap into the Great Gate as soon as possible, which means staying close to where it would open. Since Martin doesn't die while you're in there, that minimizes his chance of getting killed.

Buffing Martin doesn't appear to pay off compared to removing the threats, as a use of the player's time. Reverse-pickpocketing items that will protect him before the battle starts is about the only defensive thing that's worth doing, but there's not a lot that he'll use.