Thanks. I care a lot about low light but the reason for considering the m6 ii is being able to record 4k. Shame I cannot get it all.
Which of these are you prioritizing over the other -- stills shooting at low ISO's or 4K video?
As others have stated, the RP wouldn't autofocus all that well in 4K since it doesn't use dual pixel autofocus in 4K. I believe it's also a 1.7x crop in 4K. (Someone correct me if I'm wrong). So even the RF 35mm F1.8, you're at about 60mm full-frame equivalent. That is not wide at all, if wider than 60mm is what you'd need.
Personally, and this is just my opinion, I'm not a fan of 4K in this class of camera. For family videos, vacations, etc., I think the look of 1080p shot at 60fps with a shutter of 1/60th, and aperture set for desired DoF, with Auto ISO for exposure is the way to go. I have the original M6 and video shot with those settings is awesome. I rented an M6 II for a week to see what 4K was like. It's an excellent camera, but after comparing video on my M6 taken with the settings described above, compared to M6II 4K at less frame rate, I much preferred the 1080/60p. Again, all subjective.
For stills, yeah you may want to see if you can get your hands on them to do your own high ISO comparison. I was *this* close to buying an RP the other day. It's currently $999 with the EF lens adapter included, which I would have paid $100 for, so basically $899 for a full-frame camera. That's just awesome. I read and watched a huge amount of reviews and while the camera was generally universally loved at that price point, the one thing that kept coming up in my research was the high ISO performance was not what you might expect from a full-frame sensor. Now this is just a bunch of random web reviewers, but it came up enough that it made me hesitate. If I'm going to upgrade for the purpose of high ISO performance, I want the ISO performance to be stellar in comparison to what I'm getting now with my M6, which I think is pretty excellent already. I didn't get the impression it was going to be a *huge* upgrade in high ISO IQ going from my M6 to the RP. I decided to wait for the next R camera, whenever that is.