My experience of this is negative, I'm afraid. I had a rock solid 1Mb connection, but decided to move to another ISP, with more competitive prices for the same service. However, when I rang for the MAC code, my current ISP convinced me that I could receive "up to" 8Mb on my phone line, should I stay with them and upgrade to their Max package, at just £1 per month more then I was paying at the time. The temptation was too great, and it was also a lot easier to stay than to go, so, with hindsight, stupidly, I agreed to the "upgrade", and to a further year's contract.
On the day of my upgrade, my connection speed suddenly shot up to 5.8Mb!! However, as I expected, there is a stabilisation period of about 10 days, while BT's software configures the best stable line speed, and my connection kept dropping, and also slowing at each reconnection, until about 2 hours later, when it seemed to stabilise at about 4.1Mb. This would have been great had it remained that way, however, over the next few weeks, my line speed gradually reduced and reduced more, and I am now connecting at a pathetic average of about 1.2Mb. I have been onto my ISP several times, each time having to wait up to 40 minutes in a call queue, and they have raised the issue with BT, but have now admitted my line was never capable of speeds over 5Mb, and realistically, I should consider anything over 2Mb as bonus! BT are supposed to be upgrading my exchange during November, so I am now waiting to see the outcome of this. but at the moment, I feel totally stitched up, and am only getting a barely significant increase in my line speed, and am paying £1 per month more for it, when I could have gone to another ISP and saved about half the cost.
Don't let me put you off, Debs, this is just my experience, but I would advise extreme caution where the words "up to" and "possible" are used. My ISP promised what they could not possibly deliver, in order to retain me as a customer, and I fell for it. I could "possibly" win "up to" £1Million on the lottery, but if I spent £1000 on tickets and didn't win, I wouldn't have any recourse, because there were no guarantees that I would win. Broadband is an extremely competitive market, and, in my opinion, the ISPs will do anything to retain customers. "Up to", "possibly" and "estimated" mean jack sh*t when it comes to ISPs delivering the services they advertise, but is an excellent escape route for them, when services don't live up to customer expectations.
I'm not saying that slow line speeds are always the fault of the ISPs, but they should not deceive customers with promises they cannot possibly deliver, using "up to", "possibly" and "estimated" as a get out clause. I'm not saying don't do it, Debs, just be careful. I still have a rock solid connection, but I was fooled into signing up for another year with my ISP, having been led to believe I could receive a much faster connection, at a time when it was never possible.
I should also clarify that my ISP is NOT BT, so they, if anyone, should be able to judge more accurately what services they can provide, and at least you should have some comeback if it all goes wrong.