Rather than samknows, try this:
http://www.dslchecker.bt.com/adsl/ADSLChecker.AddressOutput
You can stick in the post code and it will give you the list of houses which you can choose from, or if you know the number you can use that. It’ll tell you if fibre really is available, as well as estimated speeds for that and ADSL services from BT. For a lot of rural houses the cabinet can be fibre enabled, but the copper is too long to support VDSL so it makes no difference…
Once you have your estimated speed, all providers are going to be the same pretty much, as they are likely all to be using BTs network to get to your house. The main difference is price, and the quality of service they provide – how much bandwidth that they have between them and the internet, is it enough to meet the demands of all their customers.
I’m in a similar situation – looking to move to the sticks – the cabinet is fibre enabled by several K from the village so I’m stuck with 2.5meg DSL. If the move happens I’m going to investigate setting up a point to point wifi link to somewhere that can get a decent connection!