not so much stacked but when everyone is in a small amount of space it will lag, because of the stress it would do. So remember this, anytime you lag it maybe because you are in a area where there are more players then normally which strains your video card.
Technically our eyes can see an average of 30 fps, you really can't see much beyond that because our brains and eyes can't process that many quickly. But what does happen is the player will run more smoother and you will also feel like "floating", I'm sure when this game just came back everyone felt the game as being "floaty"... thats because most of us have were getting high FPS and not use to it because the game doesn't have to much to render unlike other games.
I believe if you are around 60-100 fps you are doing very good, anything higher really won't make too much of a difference. Your ping on the other hand...