Congrats on the R6 Mark II! You are gonna absolutely love that 40fps burst for birds in flight. Honestly, it is a game changer for getting that perfect wing position! Since you are hitting those crazy high speeds, the card speed really does matter more than you think. If you go with a V60 card, you will definitely feel the camera chugging while it tries to empty that buffer after a long burst. Its super frustrating to see a cool behavior happening while your red access light is just blinking away... Basically, V90 cards guarantee a minimum sustained write speed of 90MB/s, which is vital when you are dumping 40 RAW files a second into the buffer. While the R6II has a decent internal buffer, it fills in just a couple seconds at max speed. A V60 card only guarantees 60MB/s, so that extra 30MB/s headroom with V90 actually makes a massive difference in how quickly you can start shooting again. If you want the best performance without spending your entire $200 on a single card, you should check out the Kingston Canvas React Plus 128GB UHS-II V90. It is fantastic because it gives you that V90 speed for way less than the ProGrade Digital SDXC UHS-II V90 Cobalt series. I have used the Kingstons for a while now and they are amazing for wildlife. If you really want to stick with the big names, the SanDisk Extreme Pro 128GB UHS-II V90 is solid too. Ngl, you wont regret having the fastest write speed possible once those birds start moving!