honestly, v30 cards are just not gonna cut it for 4k 60p on the r6 ii. i had issues with this same setup last year and it was a total nightmare. unfortunately, those older cards just cant maintain the sustained write speeds needed for the higher bitrates canon uses. the v30 rating only guarantees 30mb/s, and your camera is trying to push way more than that during high frame rate recording. thats exactly why you are seeing it crash and stop. if you want to stop the errors, you need at least v60 cards. here is what actually works based on my experience:

• ProGrade Digital SDXC UHS-II V60 Gold 256GB - these are my top pick. they are super reliable and i havent had one fail on me yet during a shoot. they handle the r6 ii data stream without breaking a sweat.
• SanDisk Extreme PRO SDXC UHS-II V60 128GB - a decent choice, though unfortunately i have seen some quality control issues with sandisk lately so they arent as good as expected sometimes.
• Lexar Professional 1800x SDXC UHS-II V60 - these are usually priced well and i have used them as backup cards for weddings without any dropped frames. basically, the v60 rating ensures a minimum 60mb/s sustained write, which is the baseline for stable 4k 60p on your body. v90 would be better for absolute peace of mind, but for a 200 buck budget for a pair, v60 is your only realistic path to stability. dont risk a wedding gig on v30 glass... its just not worth the stress.

Adding some technical data here because those recording errors are basically just a math problem with the write speeds. Since youre shooting 4k 60p on the R6 II, the bitrate is about 230Mbps. On paper, a v30 card should handle 240Mbps, but in reality, heat and file overhead mean they dip below that 30MB/s threshold way too often. Thats why the buffer chokes. You really need a v60 rated card to have safe headroom. If you want to stay under that 200 dollar limit for a pair, I would look at the ProGrade Digital SDXC UHS-II V60 Gold 128GB or even the SanDisk Extreme PRO SDXC UHS-II V60 256GB. Both of these have much higher sustained write floors. I usually check the database at Camera Memory Speed or the SD Association whitepapers to see how these cards actually behave under load. ProGrade is usually my pick because they seem to handle the heat of long wedding days a bit better. Just be careful not to buy the older v30 version of those Sandisk cards since the labels look almost the same. Moving up to v60 gives you a 60MB/s minimum which is double what your video stream actually requires. Should stop the crashing for good. Let me know if you need help looking at any other specific models before the big gig.

Unfortunately, I went through a similar ordeal when I first started pushing 4k 60p. It is a real shame that these expensive bodies dont come with more reliable internal buffers to handle slower media, but that's just the reality we're stuck with. I spent way too much money testing cards that claimed high speeds but failed under the constant heat of a long wedding day. Its incredibly frustrating when a card looks good on paper but thermal throttles after twenty minutes of recording. If you're trying to keep the total for a pair under $200, you have to be really strategic. V90 cards are usually overpriced for what they offer unless you're doing high-end All-I video, so stick with high-quality V60s. Here are the ones I found to be the most cost-effective without sacrificing the reliability you need for a Chicago wedding:

• ProGrade Digital SDXC UHS-II V60 Gold 256GB - these are my go-to recommendation because the sustained write speed is actually consistent. You can usually grab a two-pack for right around your budget if you find a sale.
• Kingston Canvas React Plus UHS-II V90 128GB - honestly, these are some of the cheapest V90s out there. If you catch a deal, you can get two for under $200 and they handle the R6 II bitrates easily.
• Sabrent Rocket SDXC UHS-II V60 256GB - a bit of a sleeper pick, but theyve been reliable in my experience for long-form video. Keep in mind that heat is your biggest enemy here. Even with a good card, the R6 II gets toasty during long sessions. I usually buy from B&H or Adorama to avoid the counterfeit issues on other sites... had a fake card die on me once during a speech and i'll never risk that again.