You can use rsync to give an approximation of your transfer speed, although it will vary depending on whether small or large files are being transferred and whether the destination is a slow flash drive or a fast external hard disk. For example:

rsync -avviu ~/Videos /media/Mik2



sent 874419803 bytes  received 149 bytes  4427442.79 bytes/sec

total size is 874312527  speedup is 1.00

(Also, if you open tail -f /var/log/kern.log and then connect your device you can see whether it is being set up for ehci (enhanced host controller interface), which supports USB 2 speeds. For example, the kernel log should state 'new high-speed USB device...using ehci_hcd'.)