Very interesting to see the Speed Ranges for the various Postcodes, especially EX8 4NS.
My app uses the BT DSL Checker and it calculates the best and worst speeds creating a range, that's why it has a very low speed and the 80Mbps as the top speed.
So one end must of been low and the other high, ill will do a speed check of that postcode and send you a PM of the actual individual speeds.
Paul