Simply a quick

I can only confirm Arcade's answer: Kingston Canvas React Plus
- no problems so far
- "swallows" my 40fps from the R6M2 very fast
- never problems with the Safeprotect slider (unlike other cards)
- very good price-performance ratio

After a lot of research, I bought the Kingston Canvas React Plus. Type SD XC v90 II. Top product, very fast.

I only use Angelbird cards and am very happy with them.

I use two SanDisk ExtremePro SDXC 128GB U3 UHS-II and two Kingston Canvas React Plus SDXC. One of each brand in each SD slot, so there are two different cards.

I can also confirm that you need 300MB/s (V90II) for flawless recording if you are recording on 4K on frame rates higher than 25p. Up to 25 V90I is enough - never had any issues, even with CLog3 with Cinema gamut. In the camera manual there is a table of the bit rates per video format.

Sony SF-G series TOUGH SF-G64T 👌🏻

I've been using SanDisk for their flawless reliability for over 25 years. I regularly record concerts lasting between 60 and 90 minutes. To avoid clogging up the R6 mk II buffer during long 4K recordings, you need a very fast hard card recording speed. I've tested some cards with speeds of less than 300MB/s, and in these cases, recording sometimes stops for 1 or 2 seconds to empty the buffer before resuming. So I use SanDisk Extreme Pro 300MB/s SDXC (SDXC, 256 GB, U3, UHS-II).