Well comparing the DP review images, the differences really shrink. I am having the darndest time telling them apart! I also compared them with the R3 reduced to 1Dx III dimensions and I can't tell them apart with my eyes.

Detail is better with the R3 at full resolution, which is nice. But not game changing.

Big thing is actually using them side by side and post processing them. But even then I doubt the difference would be huge.

All in all just like it has been said, IQ is marginally better. But everything else that makes the picture taking better is promising to be very good.

And one nice perk you are actually $500 less.

The other aspect of it is the RF 85mm f/1.2 is an incredible lens by all accounts. Having used it at the wedding it definitely is much faster focusing and much sharper. Which is huge deal for weddings and portraits. So it's not just about the camera all the time but the lenses you can use.