For the R5, you absolutely want to get a CFexpress Type-B card for slot 1 if you're serious about getting the most out of this camera. If you want to shoot in 8k or 4k with the higher bitrate settings then you will require a CFexpress Type-B card. I've been using my R5 for wildlife photography for 2 years now and the CFexpress Type-B cards will definitely clear the buffer the fastest and are therefore ideal for shooting fast bursts of images like you would shooting sports or birds in flight.

I personally use the SanDisk Extreme Pro CFexpress cards, though the top 18 CFexpress Type-B cards all performed extremely well and although some cards are marginally faster than others, in the field you are unlikely to notice any difference at all. Our advice would be to purchase whichever card is offers the best durability and warranty and not simply the cheapest cards

Totally agree that CFexpress is the only way to go if you want to unlock the full potential of the R5, especially for video. But tbh, the cost is definitely a sting. One thing I've found that helps the budget is using a dual-slot strategy where you save the *expensive* card for your high-bitrate video or fast bursts, and use a standard V60 or V90 SD card in the second slot for redundant photo backups. It’s basically the best of both worlds without needing to buy two high-capacity CFexpress cards lol. Also, if you’re just doing standard 4K (not HQ or Raw), the SD slot is actually more capable than people give it credit for. I'd definitely suggest looking into some of the newer manufacturers that have entered the market recently, as they've really helped bring the price-per-GB down compared to the big legacy brands.