Honestly, those 30MP files will literally choke ur buffer if ur cards are slow... I've had it happen and it's pretty bad. Basically, prioritize speed: - SanDisk 128GB Extreme Pro CompactFlash Card 160MB/s
- Canon LP-E6NH Lithium-Ion Battery Skip the grip; it's way too heavy for 10-hour days imo. gl!

Just sharing my experience: I went through this same struggle when I first started shooting 10-hour events with the 5D IV. Those 30MP files are actually MASSIVE, and while everyone says go for the most expensive cards, I found a middle ground that saved me a ton of cash. I basically compared using high-end CF cards versus fast SD cards for redundant backup. * Option A (The Buffer King): I ended up using the Transcend 128GB CompactFlash 800x (UDMA 7). It supports UDMA 7 which is huge for keeping that buffer moving during long bursts, and it was way more affordable than other "pro" brands.
* Option B (The Backup): I paired it with a Kingston 128GB Canvas React Plus SDXC UHS-II. Even tho the camera slot is only UHS-I, having a fast V90 card made offloading to my workstation SO much faster at 2 AM.
* Option C (Power): Instead of a bulky grip, I used the Wasabi Power Battery (2-Pack) and Dual USB Charger for Canon LP-E6NH. In my experience, the grip weight just wasnt worth it for the ergonomics, right?

Saw this earlier but just now getting a chance to reply. Technically speaking, you dont need to break the bank on the big brands to get pro performance out of the 5D IV. Since the SD slot is only UHS-I, buying expensive V90 cards is basically throwing money away because the hardware bus is a bottleneck. I usually suggest the Samsung PRO Plus SD Full Size 128GB because its cheap and rock solid for redundant writing. For the CF slot, the Silicon Power 128GB Cinema PRO CF 1066X is a hidden gem... it hits the UDMA 7 specs perfectly for a fraction of the cost of the big names. If youre worried about the battery life for those 10-hour days, skip the OEM prices and grab the Powerextra 2-Pack Replacement Canon LP-E6N kit. They show the battery percentage correctly on the 5D IV screen which some cheap brands dont do, and having a dual charger that runs off USB is a lifesaver in the car between venues. It definitely beats carrying the heavy grip all day imo.

So, coming back to this after an hour or so, it is cool to see the different takes. From a market perspective, the 5D IV is in a weirdly great spot right now because the EF ecosystem is so mature. You basically have to choose between the legacy pro-grade brands and the newer high-performance manufacturers that are trying to disrupt the space with lower prices. I wanted to ask a couple of clarifying things before giving more specific advice:

• Are you prioritizing gear with a long-term warranty and local support, or are you okay with overseas manufacturers if the performance is there?
• Is your workflow more focused on high-speed bursts during the ceremony, or are you more of a single-shot precision shooter? For actual data on how different brands perform, you should check out the technical reviews on The-Digital-Picture or the gear talk over at Fred Miranda. Those guys do deep dives into things like voltage consistency in batteries and actual sustained write speeds that go way beyond what the marketing labels say. It is honestly the best way to avoid wasting money on gear that looks good on paper but fails in the field during a 10-hour wedding day.

For your situation, I've been thinking about the 5D IV's workflow and honestly, it's a total workhorse, but it definitely has its quirks with those huge 30MP files. For CF cards, you really gotta look at the UDMA 7 rating specifically to keep that buffer clear during bursts. I would suggest the Lexar Professional 1066x 128GB CompactFlash Card as a solid, high-speed alternative; it handles the write speeds for those RAWs without many hiccups. Regarding the Canon BG-E20 Battery Grip, I'm actually gonna suggest it for weddings. Tbh, even though it adds weight, the vertical controls are basically life-savers for ergonomics during a 10-hour day. If you're worried about the bulk tho, just make sure to use a high-quality strap like the Peak Design Slide Camera Strap to distribute the load across your shoulder. Also, definitely grab a GGS Larmor Gen5 Glass Screen Protector for Canon 5D Mark IV—it's a hidden gem for protecting that touch screen from belt buckles and snaps. Just be careful with off-brand batteries; this body can be kinda picky about power reporting. gl!