jolyonralph said:
The 85 1.2L has a characteristic "look" that I don't know if the 1.4L IS would match. I haven't shot both, but I own the 1.2L and I'm pretty happy with it.
And what I should have added to my previous post is that the real choice between the two should be which one you like better for the pictures it makes, rather than small numbers on one's calculator. Up to a point, a little softness in a portrait lens is often considered a feature, not a bug.
On my Rebel I used the 50mm f/1.4 as my portrait lens. Now with my 6D2, I consider the 100mm macro to take that role. I have made some rather nice portraits with the 24-105mm STM, but it opens just to f/5.6 in portrait range, so no extreme background separation. Early in the spring I was taking some macro shots of flowers in the front yard and got into a discussion on lenses with a neighbor. I took some shots of her and her cats that turned out well. In the pictures she does seem to have more freckles than in real life, and one of the cats looks fiercer with her fangs bared. In real life she looked more like she was smiling. She certainly was not acting threatened or aggressive.
Later I needed to send a recent picture to my alma mater for an "annual" they are making for our class reunion. So I set up the tripod. Took the dead batteries out of the flash. Decided to use ambient light rather than taking time to clean out the corrosion from the dead batteries. Set a 2-second delay for me to pose after I hit the infrared remote, and made a series of pictures as I stood in front of an empty neutral wall in the hallway as I looked into the flippy screen for positioning. My that macro lens is sharp! It made me look like an old man, mainly because I am one. I can see more detail in my skin in the pictures than I can see in the mirror after cleaning the mirror. The diffuse light did soften the bags under my eyes, and Photoshop helped a little more. In posing I opened my eyes more than I do in real life even as I smiled gently.