To add to the point above: I agree that the buffer handles a lot of the heavy lifting. Unfortunately, I found the pricing on some high-end cards to be not as good as expected when you look at real-world results. I had issues with overpaying for V90 cards that didnt feel any faster than V60 in my daily workflow. Here is a more cost-effective approach for your new camera:

• ProGrade Digital CFexpress Type B Gold 512GB is a solid middle ground that wont break the bank like the pro series.
• Sabrent Rocket CFX 512GB CFexpress Type B offers some of the best price-to-performance ratios for 4K recording.
• ProGrade Digital SDXC UHS-II V60 Gold cards are significantly cheaper than V90 versions and still provide plenty of speed for backup files. Basically, dont feel like you have to buy the most expensive thing on the shelf to get good results. Using V60 for the SD slot is a much better way to manage your budget.

CFexpress Type-B cards are recommended.

CFexpress Type B Card Slot: Lexar Silver SE or Angelbird

UHS-II SD Card Slot: SanDisk Extreme Pro UHS-II V90 SDXC

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Same here!

Lexar CFexpress Type-b Silver SE card is recommended.

I've tried many cards over the years with these high-resolution bodies. In my experience, the sustained write speed is much more critical than the peak speed listed on the packaging. For the primary slot, the Delkin Devices 650GB POWER CFexpress Type B is an excellent choice for the R5 Mark II. It handles the high bitrate of 8K video without the overheating issues I've seen with some budget brands. For the SD slot, the Sony TOUGH 128GB UHS-II SDXC V90 is basically mandatory for me now. The design is much more durable since there are no plastic ribs or write-protect switches to snap off. If you want more technical data, I always recommend checking the Camera Memory Speed website. They run methodical benchmarks that show how cards perform once the cache is full. It's a great resource to make sure you arent overpaying for marketing specs that dont hold up in the real world.

UHS-II V90 cards are also OK.

Any best selling CFExpress Type-B cards are OK.

Don’t overlook the importance of reliability when choosing a memory card for the R5 Mark II. I’ve had great experiences with Angelbird AV Pro CFexpress cards. They’re built for professional use and have excellent heat dissipation, which is important for long recording sessions. Pair one of these with a high-speed SD card in the second slot for backup, and you’ll have a solid setup.

I use Lexar Silver SE CFexpress Type A card.

I use Lexar Professional 128GB CFexpress Type B Silver series cards that I caught on sale - they're more than fast enough for 4K and stills work. For the SD slot, any UHS-II V60 card works great as backup. The camera's buffer is so good you probably won't notice the difference unless you're pushing it to extreme limits.