I think "everything" will be hard to hit under pressure, if you dont practice to do it, and have it down beforehand. If you dont practice the head shots, they probably will be a problem, just like the COM shots you didnt practice while moving, or drawing and firing from concealment, etc. The less you practice realistically, the more it will show, under any kind of pressure. Everything you can work out beforehand, allows your brain to work on the important stuff without having to worry about it too. Do you think about the presentation, or breaking the shot, or do you just think "guns" and do it?
I just dont see wasting rounds on the pelvis, if thats not going to stop the fight, which I dont believe it will if your opponent is the least bit determined, why waste the ammo? Would you stop shooting if you were hit in the pelvis and went down? To me, that part is the clincher. Both targets are about the same size, both may be moving, and one will likely stop the fight, where the other just has a higher chance of prolonging it, even allowing your opponent the opportunity for just a lucky (for him) shot. He may be down, but theres a high probability, hes not going to be out.
As far as "pressure" goes, it is what you make of it. The whole purpose of working things out ahead of time is to short circuit or redirect that response and allow your brain to work on the problem at hand with less distractions. A gun fight is no different than any other kind of fight (or stressful problem). You go into it with what you have and deal with it as best as you can with what you know. Other than certain "thresholds" crossed, there really is no "plan", as there really cant be. You act/react as it unfolds.
Experience and knowledge tends to reduce pressure and enhance confidence, making things go a little easier. Time is basically irrelevant, as it takes what it takes, and if youre worried about beating the clock, youre likely to beat yourself worrying about the clock. Concentrate on doing what needs done, and do it right the first time. Rushing and screwing up, is worse than being slow and sure.