Description. The SanDisk 64GB Extreme PRO UHS-I SDXC Memory Card is compatible with the UHS-I bus, and features a speed class rating of V30, which guarantees minimum write speeds of 30 MB/s. If your device does not support the V30 standard, this card also supports the U3 standard, which likewise guarantees minimum write speeds of 30 MB/s. Read speeds are supported up to 200 MB/s and write speeds max out at 90 MB/s.