I've noticed quite a few times I have destroyed drives on a NPC, which then leaves me in the dust as it flies away.
I think if the ship is boosting when you hit the drive, the speed doesn't bleed off like it normally would (should.) Given the game favours gameplay over realism, I'd consider this little chunk of realism to be a bug (ships with no engines should probably lose momentum gradually - if smaller engines have smaller lower speeds, it stands to reason that ships with broken engines should not be able to maintain their speed. They certainly shouldn't stay at boosted speeds, like they current seem to be able to

)
I would question NPC cheating. After a number to battles near stars, where I am having all sorts of heat problem and yet NPC flying past me to star and turning around then continuing to fire.
Different ships perform wildly differently in terms of heat management (e.g. I had a T6 which tried to catch fire whenever I so much as looked at a star. Now I'm flying a Clipper, and I can't seem to turn up the air con, it's an ice box in here.)
I would expect AI ships to be subject to the same rules on heat as player ships (after all, this is supposed to affect targeting, so it's pretty relevant even outside of the edge case of fighting near stars.) It'd certainly be nice to know for sure.