i) I don't know, but it probably would;
ii) This depends on your philosophy. Assuming you are on the boarder between the two, there is not much difference between being at the back of A v. the front of B. I would think the biggest advantage by far is that you would not need to worry about getting to the front of the corral. You could take your time, maybe warm up more, and just slip into the back--which would be great.
I would just try to avoid any temptation to move up to the front of A. Ideally you want to start the race relaxed with people of the same pace. If you get too far up you risk going out too fast (as 95% of most people do).
I would try to get into A for no other reason than not having to fight to get to the front of B.