I have been photographing with a Canon 80D for about 4 years, mainly birds in flight, and got the itch to upgrade. I ordered a Canon 90D from B&H and used it for about a month. I had nothing but problems with getting focus on birds in flight. Did all kinds of changes to the custom settings, but didn’t help. I went to the Canon 90D Facebook page and there were countless postings of people having problems with focusing on birds in flight. I returned the 90D to B&H and order the 5D MKIV. I have been using the MK IV for about 2 weeks now and LOVE this camera.

I think you would do well with the newer 1DX series. Even though I shoot Olympus now, I have shot with Canon at one time. It is a good system and I suspect that the larger pixel size on the 1DX might help solve the noise problem you are seeing. If you are not making a lot of larger than 30X40 prints, it probably will sever you well. I know my 20MP Olympus E-M1 mkII serves me very well and it would have more problems with noise than the 1DX series would. As worst case, rent a 1DX and put it to the test of your photography.

I looked at some of you work from safari. Not all the images where stored with the EXIF data. You might be better served starting a separate discussion on (a) low-light technique and (b) high ISO processing. Your observation about the same sensor is spot on, the 1 to 1 results should be similar, if not indistinguishable between the cameras. I did a sort by ISO in my LR catalog for comparables, but I don't have anything in 2019 / 2020 that really matches based on light and distance looking at your results. You might consider another separate thread based on your dog running results where AF tuning ideas (or limitations) specific to the EOS R might be discussed.