No matter how hard I try to maintain posture through impact, I still end up "standing up." I'm coming over the top, too, so I'm guessing those are connected in some way, and I have no idea where to start in terms of fixing it.
160 is what I consider the stock distance (not carry) of my 5 iron as well. And like you, the potential for >180 is always there, especially off the tee.
While getting extra distance is cool, I'd prefer to get closer to my expected distances - at least from good lies. Even if I miss left or right, it's a good feeling to know i pulled the correct club and got the desired distance on an approach shot.