I've disabled replays like a year ago and it truly makes game a lot smoother, at least for me (10-15 more frames depending on the map). The major problem now is poor UI. UI is very very slow in this game for some reason.
I do get freezes every now and then but I think that's because of my connection. I don't know if disabling replays will stop game from freezing like this.
Disabling ingame movies help with the main menu sluggishness.
My guess would be that it is poorly coded flash (scaleform) or just flash in general since there is so much going on in the UI.