Went from crop to FF. Night and day with the 85L. Only with FF one can appreciate the 85L, believe. Colors. I used to think "I must think I like the colors and look of the pictures taken with the 85L because it costs a lot" but then my mom comes along and says "wow, beautiful colors on that and that photo". Picked one by one the ones shot with the 85L, and she knows nothing about lenses. Then I knew the 85L is indeed a special lens. Not my first choice on a set of lenses (that would be my 70-200 2.8L IS mkII), but if one can afford one and its time to buy a 85, go with the L, you can´t go wrong.
Just know the AF IS slow. But that´s part of the lens, just like one can not say "MP-E 65? hard to focus, choose another" while it´s true, there is no other like it. Know the lens, master it (I´m far from that). Part of the fun is the challenge.