The game is broken, valve releases update after update with nothing but new cosmetics, none of them with a single bit of performance optimization. You seem to have done enough, but 120fps is unlikely to happen for you in fights with a 4890 nowadays.
I own a 660Ti and get 150fps in some mid fights. I owned a 570 before and was getting more fps tho, I think this current nvidia generation isn't really optimized for source engine games (570 peaked 2000 fps in some maps, 180fps in mid fights). Also, source engine is very cpu bounded.