v1 / v1.1 = 12mbps or 1.43mb/s
v2 = 480mbps or 57mb/s
v3 = 4800mbps or 572mb/s
If your using a USB hub, this can reduce speeds due to the way they redirect data.
To get a little more performance out of a hdd's or usb flashdrive/hdd, if you go into device manager, expand your list of flashdrives/hdds and right-click, choose properties, policies and then tick the box to switch off write-caching buffer flushing.
Please be aware that you cannot just unplug a usb device with this active as you could loose unwritten data, you must use the usb icon found in the system tray and eject the drive.