My 85mm 1.2L II focused significantly better on points outside the center (though not at the very edges) on the 5DIV than it did on the 5DIII; however, I still wanted snappier AF plus IS, so I traded it in for the 1.4L IS. I think it was the right move.
I would have thought the 50mm 1.2L would work better on the 5DIV also. Sorry to hear that isn't the case for you. Please follow up if you do try it on an R body!
I've found the the 85L f/1.2L II focused well on the 5DIII and better on the 5DIV. With both bodies, the 85L II and the 85 f/1.4L focused better than the 50L with the outer AF points. I was tempted when there was a Canonpricewatch deal for the R, but I'm looking for something at or above the 5D level.
I'm definitely interested in trying one out when they're available in the local camera stores.
While these lenses are welcome updates of Canon's highest end EF lenses, they were likely in the pipeline for some time. I also expect that some of the updates help these lenses work better with the RF adapter, as Canon has already said that lenses released before 2012 will not take advantage of all available RF features.
The same tweaks for better RF performance might explain the strange case of the 70-200mm IS III update, which, otherwise, seems to be only a new paint job and less resilient lens coatings.
To repeat yet again, few posters here, if any, have claimed that Canon would immediately shut down production of EF lenses. I'm a Canon customer who believes that EF as the flagship, central lens mount for Canon is now in the rear view mirror. Yes, updates that cut production costs of existing, popular and very profitable per-unit lenses (such as the big whites) will still be released for a year or so. As said, these are clearing the pipeline during the transition to RF.
I think those who claim "hysteria" or "bias" against those of us who believe EF is now a legacy tech are actually arguing against a timeline, not a concept. Will the last EF lens be produced two years from now? Probably that is too soon. Five years from now? In my opinion, quite possibly. But, once again, EF lenses will be serviceable and worth buying after production officially ends because there will be many working EOS bodies circulating for many years beyond.
I think people who don't believe that RF will replace EF don't believe Canon has actually come up with something better, or that Canon would ever phase out something that has been around for 30 years even if RF is better for them and customers.
But I've also admitted in this thread that I might have overestimated the speed at which Canon is actually capable of making the transition, especially after reading the article with the general managers who claimed they simply didn't have better sensor tech or IBIS tech ready for the EOS R.
If calling my thought process "bias" makes you feel more comfortable during a time of exciting transition, that's ok. I will repeat my thanks to those posters here who have patiently explained why they believe EF lenses are still, generally, a good buy for quite some time.