Hi Andi,
The theoretical maximum is 21.6Mbps Download and 5.7Mbps Upload.
These are theoretical figures and you will never actually see there. As you seem fully aware the speed you get very much depends on the area you are in.
When I had one on loan i was getting around 3Mbps download and about 1.5Mbps upload(actually faster than my fixed line broadband).
I was using it in and around Aberdeen city most of the time so I almost always had a good 3G connection. I did use is a couple of occasions on the train to Elgin where the device did cope surprisingly well with the poor/no coverage.
I thought it was a great little device and if i were to continue travelling (as i was at the time) I would be purchasing one for myself, especially now the price has dropped!
EDIT: There is a pretty good review of it on the pcadvisor website if you were interested.
