Don't bother !
I swapped to Infinity (only because the cost of my copper braodband - which was perfectly satisfactory - was 50% higher and they would not reduce the price).
I had three months of trouble when barely a day passed without me losing service. I had to endure four or five visits by an engineer. It was finally put right but I had terrible trouble with BT's customer (don't)care department to squeeze some measly compo out of them.
The speed difference (although about eight times as fast) is of little significance for everyday use. All in all a waste of time and a lot of bother.