I just looked at the noise comparison, didn't realize Bryan already did the leg work.

I think it is interesting to note unless you are shooting at 100k ISO where the R6 takes a lead. The R5 looked ever so slightly noisier but also better detail. With noise reduction on at say ISO 6400, the R5 actually looked just the tiniest bit cleaner and ever so slightly better detail. This was the PS comparison, DPP was not quite as good.

In other words there was more difference between the software used and what settings and technique used than the difference in the two bodies. Partly there could be differences to mitigate it when Canon made them. But that is purely a guess on my part.

The R5 definitely compares well unless you consistently shoot at 100,000 ISO. And even then I would say it is roughly a 1/3 to 1/2 of a stop. But I believe that is because the R6 has a higher native ISO. So you are pushing the exposure an extra stop. But even at 51,000 and with noise reduction you are splitting hairs.

All this to say there is not a one stop difference in noise performance if you are making a fair comparison.