I recently upgraded to the Panasonic Lumix S5 II, and I'm loving it so far. However, I'm a bit overwhelmed by the memory card options available. I know the camera has dual UHS-II SD card slots, but I'm not sure which cards would be best for optimal performance.
I suggest you to get a UHS-II SD card, for example: SanDisk Extreme Pro UHS-II V90 SDXC.
A V60 256GB SD card works perfectly with the S5II, supporting all recording settings, including 6K open gate. I achieve about 2 hours 30 minutes of recording on one card. V90 cards aren't necessary for this camera's performance.
The Angelbird AV Pro SD V90 cards are excellent with the S5 II. They're a bit pricey but worth it if you're doing serious video work. I've tested them with 6K 30p and they perform flawlessly. Get at least 128GB since those video files get large quickly.