Yes.
It's the same whether it's plugged into the computer or whether it goes via the router (Edimax 3G-6200n)
The downstream is pretty solid (5.4Mbps) despite the router only reporting a signal strength of 47%
The positioning does matter greatly. The upstream is more picky; it won't go above 1Mbps unless it's exactly right when it will stick at about 1.5Mbps.
Average ping is about 70ms.
With regard to the faster speeds - if I saw it hit say 7Mbps of the 7.2Mbps that the Edimax supports, then I'd think it was the choke point. However I did come across this bit of text on the ADSL24 website:
http://adsl24.co.uk/broadband/mobile/
When talking about Mobile Broadband speed, mobile operators refer to the theoretical maximum speed, known as the technical standard. In reality, it's not possible to achieve this speed and we want to be honest with you about what you can expect. Even though the network's theoretical maximum speed is 7.2 Mb, you'll actually experience up to a maximum of 5.6 Mb
Which suggests I'm getting the maximum available (or near as) and although I am getting an antenna put up on the chimney next month I'm not expecting huge gains (no pun intended).