just sharing my experience: i went through this last year. i've been shooting wildlife for decades and tried to cheat the system with slower cards first... * Sony SF-M Series Tough UHS-II V60 128GB: great value, handles 4K 60p fine but lags on 30fps bursts.
* SanDisk Extreme Pro SDXC UHS-II V90 128GB: pricey but clears the buffer fast. lesson learned: i found v60 is a budget sweet spot, but 30fps kinda demands v90 speed tbh

Seconding the recommendation above! Honestly, the ProGrade Digital 256GB SDXC UHS-II V60 Gold Card handles 4K 60p easily, but for 30fps bursts, you kinda gotta get the Kingston Canvas React Plus 128GB SDXC UHS-II V90 Card. It's literally the cheapest V90 and the 285MB/s write speed clears the buffer way faster than V60!! Best value for wildlife imo. gl!

I totally agree that for wildlife, trying to "save" money with V60 cards usually ends in regret. The R7 pushes a ton of data, and that 30fps mode fills the buffer in just a few seconds. If you look at the current market, you don't actually have to pay the premium "big name" tax to get top-tier V90 performance anymore. I’ve been tracking prices and the Lexar Professional 2000x SDXC UHS-II V90 is a total beast for clearing that buffer quickly; it's often significantly cheaper than the top-end Sony equivalents during sales. Another sleeper hit is the Sabrent Rocket SDXC UHS-II V90. It’s surprisingly affordable for the speeds you get and has been rock solid in my experience. Honestly, even though V60 is technically "enough" for the 4K 60p bitrate on the R7, it’s that *instant* clearing of the RAW buffer after a burst that makes the V90 worth the jump. If you're missing the next sequence of action because the red light is still blinking, the card hasn't done its job. If you're on a budget, maybe check out the Angelbird AV Pro SD MK2 V90 as well—they have great sustained write performance which is exactly what the R7 needs when it's dumping those 32.5MP files.

oh man, i feel u on that buffer struggle!! so basically, when I first took my R7 out for some birding, I used my old cards and it was a total disaster lol. I was tracking this hawk and then BOOM - the camera just stopped and I had to wait forever... seriously missed the best shots. Anyway, here is what I recommend looking into:
* Go with SanDisk, you cant go wrong.
* Just get any UHS-II V60 from a big brand like ProGrade. Honestly, you probably dont NEED the expensive V90s, but you definitely gotta have UHS-II. I mean, V60 is usually the sweet spot, though I'm still kinda learning how the write speeds affect the 32.5MP buffer clearing. Just be careful with random brands cuz they can be super glitchy with high-res video recording. but yeah, definitely ditch the UHS-I stuff. gl!!

I've been thinking about your dilemma while looking through my own archives from last weekend. In my experience, the R7 really tests the limits of the UHS-II interface more than almost any other body in its class. I do have one question though: are you mostly firing off short bursts of 5-10 frames, or are you pinning the shutter until the buffer hits the wall? That makes a massive difference in whether you can get away with a mid-range card. Based on the brands I've cycled through lately:

• Go with Delkin if you want something that can handle the write cycles. They've been my go-to for reliability lately.
• Just get any V90 card from a high-end brand like Angelbird. In my experience, the cinema-focused brands offer much more stable sustained speeds than the mass-market consumer ones.
• Like someone mentioned, trying to cut corners on card speed with a high-res crop sensor like this is usually a losing battle.

Exactly what I was thinking