Unless you live right in the town centre (where you can get 5-6Meg DL if you're lucky) that to even get the 2.5Meg DL I get is amazing! Most people seem to be getting between 1 and 1.5Meg outside of the town centre!
Poor speeds are probably down to ally cables that were used for a short period instead of copper when prices went silly. BB doesn't like it, they are bad enough for speech as they just corrode into white dust!
but also 3/4 of a mile from a relatively uncongested exchange - things that are normally far more important to the speeds you get than the ISP you're with.
In my experience, village exchanges (bearing in mind that normally only villages right out in the sticks will have their own exchange) are often the more congested due to lack of demand to justify investing in it. A bigger exchange is more likely to be upgraded before it nears full capacity as otherwise you get the situation where customers/ISPs are unable to apply for BB connections, and that's a bad thing in anyones book!
If your broadband speed varies and suffers during 'rush hour' then the exchange is the limiting factor, if your line is just slow all the time, its line quality.
