Cloud Chaser (and other interested parties),
You should also make yourselves familiar with the BT spec for the service :
http://www.btwebworld.com/sinet/485v1p0.pdf
The document details, amongst other things, what BT considers to be acceptable speeds for the service.
It also contains this tidbit, which all *DSL users should remember ......
Typically, the End Users require occasional fast but ‘bursty’ access to private network facilities and / or the Internet (via the Customer). The products are not suitable for End Users who require continuous bit-rate, full-bandwidth services.
(And for those of you who don't know yet, apart from the odd LLU network, BT have a virtual monopoly and supply this DSL service wholesale to the majority of DSL providers touting their wares ... hence the pointer to BT spec document).