I use the 85L on a 1D Mark IV (1.3x) and it's fine. I really think it's not noticeable on a APS-C (1.6x) sensor body. 85mm x 1.3 gives a nice 110mm, almost like old times 105mm portrait lens.
While I'm glad to see you enjoy the lens, and a 1D Mark IV (I like those as well), I do need to point out that indeed there is a lot of vignetting at f/1.2 to f/1.6, even on a 1.6x crop camera. This can be "corrected" of course, but it's there.
I have no doubt that if there is ever a version 3 of the lens, it will also have noticeable vignetting even on a 1.6x crop camera.
None of that is necessarily unusual for such a lens, or should discourage anyone from owning one. Vignetting is even something usually preferable for portraiture. I used it more for landscape, only did a few portraits.