I can only tell you of my experience but I was getting around 3Mb before Sky and Sky told me that my connection would be a max of 0.5Mb. However, posters on here told me that it goes off line stats and that Sky are using old data so I took the plunge.
My move was today and so far my connection has remained at the 3Mb mark.
sky 01-2011 Onwards
ADSL24 Great ISP!
entanet via ADSL24
BTBroadband for around 9 years until Port 80 fiasco