SHJ - I doubt very much that BT are doing anything like 'throttling' to your line, At 2 miles, the problem will lie either in cruddy 'last mile' wiring from the exchange or inside your house. Is that what you are getting at the master socket? If so you should complain to your ISP. 3mb min is what I would expect there at 2 miles, assuming the cable run is actually 2 and you don't feed via a neighbouring village!
Generally at the moment 5 is 'considered' to be the 'target' for the general public since that as a minimum more or less allows film and TV download. Personally I think we should be trying to have a bit of future-proofing and would look for 20.
Again, those on dial-up........................................