SD card SPI benchmark

8000000 Hz ok=3/3 init=102 ms avg=657 KiB/s best=659 KiB/s

12000000 Hz ok=3/3 init=85 ms avg=897 KiB/s best=901 KiB/s

16000000 Hz ok=3/3 init=85 ms avg=897 KiB/s best=901 KiB/s

20000000 Hz ok=3/3 init=84 ms avg=897 KiB/s best=901 KiB/s

SD card SPI benchmark (standard sdcard.py)

8000000 Hz ok=3/3 init=65 ms avg=442 KiB/s best=444 KiB/s

12000000 Hz ok=3/3 init=65 ms avg=542 KiB/s best=544 KiB/s

16000000 Hz ok=3/3 init=65 ms avg=542 KiB/s best=544 KiB/s

20000000 Hz ok=3/3 init=66 ms avg=541 KiB/s best=544 KiB/s