Just upgraded to Infinity from copper and speed tests are showing in excess of 50 mbps download and just short of 10 mbps upload. That's a 6 fold increase in download and 10 fold increase in upload speed. Add to that the current offer and I'm paying less for the new service than I was for the old, slower one.
Yes I did get a great deal DavidM, and it was purely by chance. I'd had a problem with my copper service and an engineer came to sort it - great guy can't fault him in any way. He checked the link from the house back to the 'box' on the road and said what speed I would be able to get. At that point I didnt' realise that BT had an offer on for upgrade, but took their hand off when I realised it would be free for the next 18 months.