I have the 70-200 2.8 IS, which worked pretty well for portraits. I was reluctant to spend 1870 USD on a focal length that I have already covered by a highly regarded L zoom.
Well, since I got the 85 prime, I haven't looked back. The 85 1.2L simply smokes the zoom. When I review the shots I made with the 70-200, I can't believe I once thought that THIS was sharp. The prime is sharp at f1.6 and cuts your fingers at f2.2. Add the ability the get a pretty decent hand held photo in near dearkness (room lit just by TV), add the fantastic colors and unreal bokeh and what you get is pure love. I just adore this beautiful piece of engineering.
I do keep the zoom because I find the 200mm end very useful. But I am so impressed with the 85L that I decided to get the 35L, which gets similar rave reviews. If it delivers the kind of joy I feel when using the 85L, I will sell my 24-70 and keep just the 35mm prime.