The newer UHS-1 (Ultra High Speed) Class 3 specificationrequires sustained write performance of 30MBps.
Transcend's SDXC models reach 128GB, enough for 8 hours of UltraHD video shot at a resolution of 4096x2160, with a 35Mbps bitrate and the H.264 AVC compression standard. The Extreme models top out at 64GB, though.Yes, SD card categorization is a bottomless pit of acronyms. Here are two more: SDHC and SDXC, which govern maximum capacity. SDHC models top out at 32GB capacity, but SDXC can go much, much higher.
The SDXC Extreme models cost $59 for 32GB and $119 for 64GB. The somewhat slower models cost $49 for 64GB and $109 for 128GB.
The SD Card Association's attempt to demystify the transfer-speed ratings of its flash cards.