In case anyone is interested these are the stats from a 16GB Sandisk Extreme UHS-I card in the RPi 2
Sequential Write:
root@osmc:/home/osmc# dd if=/dev/zero of=test bs=1M count=512 conv=fdatasync
512+0 records in
512+0 records out
536870912 bytes (537 MB) copied, 29.3201 s, 18.3 MB/s
Sequential Read:
root@osmc:/home/osmc# free && sync && echo 3 > /proc/sys/vm/drop_caches && free && dd if=test of=/dev/null bs=1M count=512
512+0 records in
512+0 records out
536870912 bytes (537 MB) copied, 27.1109 s, 19.8 MB/s
Random Read:
root@osmc:/home/osmc# ioping -D -R .
--- . (ext4 /dev/root) ioping statistics ---
4.91 k requests completed in 3.00 s, 1.67 k iops, 6.53 MiB/s
min/avg/max/mdev = 552 us / 598 us / 1.37 ms / 43 us
Not bad, but severely limited by the Pi I think.
By way of comparison, my Model B with a Class 10 Transcend SD card gets similar sequential read/write speeds but the random I/O is about half that (880 IOPS)