The 85L II delivers better IQ, and the bokeh is better (even with both set to f/1.8, the 85L wins for bokeh). Longitudinal CA is there with both lenses, but it's noticeably worse with the 85/1.8 (where it's really the only major optical flaw in that otherwise excellent lens). In the AF department, the 85L II is the loser - it's AF is 'ponderous' (I'm being charitable there).
For low light work, you also need to consider the DoF - yes, f/1.2 is ~1 stop faster than f/1.8, but the DoF of f/1.2 on FF is incredibly thin. Personally, I often shoot my 85L in the f/1.6-f/2.
I think the 85/1.8 is one of the best values in the Canon lineup, in terms of IQ per dollar. But...I did upgrade from the 85/1.8, and while I miss the faster AF of the non-L lens, I do prefer the 85L and have no real regrets.