I has inserted my card into a micro usb 2.0 stick and tested with a usb 3.0 input windows 8 PC. The Sandisk technical support staff has sent me his test result. The ultra micro SDXC 64Gb Class 10 has only reached a top speed of near 21mb/s with a better test set up as follows:
"Dear Ken,
Thank you again for emailing SanDisk Technical Support. It is our goal to make sure you have all the resources you need to get the most from your product. I feel very sorry for my late reply on your case.I did an experiment yesterday evening that i connected a brand-new Mobile Ultra Micro SDXC 64GB card to a USB 3.0 port by using a SD-289,the most advanced card reader with USB 3.0 interface in SanDisk.The test result is 20 plus MB/s.Please see attachmen"
