How much faster are the faster broadband services?
The roll-out of ADSL in the UK is fairly well known for its talk of contention ratios and congestion. At this point in time when most people are still on 0.5Mbps and 1Mbps services the majority of people do get very close to the maximum possible speed for their connection - this may change in the future. The Broadband Stakeholders Group in its report to the DTI collated data from a site monitoring the speed of French connections (www.grenouille.com), where speeds for connections up to 20Mbps were recorded.
As can be seen, the situation at up to around 1Mbps is very like the UK, i.e. downloads are almost the quoted speed, but once you reach 2 and 4Mbps the speeds appear to drop off. A multitude of factors can cause the effect shown, these may include contention, performance of servers offering the download, performance of end-users kit and various other variables.
So while advertising blurb will go on about connections been 10 times faster than other broadband solutions, the reality may be that you only see this speed at off-peak times. Therefore in the race for 8Mbps and faster to become common place in the UK just like in France be prepared for much larger swings in speed as your connection to the ISP gets ever faster.