At the end of the day, Mark, this isn't really a highly technical matter for which there is a definitive right and wrong, I maintain that an Internet connection is more than just your line speed to your ISP, (unless you only ever want to browse sites and downland things from your ISPs network) and a selection of speedtests at different times to different servers outside of your ISPs network will give you a much better indication of the speeds you are likely to achieve for real world use.
I personally would rather have a 8Mb/s connection that is carried right through my ISPs network and out into the rest of the world than a 50MB/s connection to my ISP and then only have 2MB/s to any location outside their network.
I'd liken it to somebody building a motorway outside your house that takes you 200meters down the road and then turns into a country lane but then you are being told you have a high speed road link to the whole world. As far as I'm concerned if that motorway is not connected at motorway speeds 200meters up the road then it's not worth having it outside your house.