SD Card Slot Speed
I have a 95MB/s UHS I and Class 10 SD card. Using Blackmagic Disk Speed Test, I get 17 MB/s write and 19.8 MB/s read speeds. Following the information in this apple support document, the speed of my internal card reader is 480Mb/s. Depending upon how you convert bits to bytes, that should be in the 57-60MB/s range.
Anyone know I can get it running at the max?