We live in the country, so don't have access to the higher speed broadband services. For years I've had a line from the business supplier Claranet. Despite being quoted at 2Mb, typical results on the speed test are 0.9Mb download and 0.2 upload. I have a second line - going to the same exchange - which I have just enabled for O2 broadband as they promised me 3Mb or better(!) It's now running, and on this site's speed test, it comes back with 4.4Mb download and 0.9 upload. Sounds like a great improvement doesn't it?
But here's the thing: I have two identical PCs on my desk, one connected via Claranet and the other via O2, so I can do a real side-by-side comparison. They are both talking to similar Wi-Fi routers in the room next door.
And, in every singly case - despite what the speed test says - real life web pages load faster with the notionally slower connection to Claranet. Same story for e-mails with large attachments.