Sorry J. I did want to answer your original qu. instead of getting carried away with the other replies.
The first thing to note is that speedos are inaccurate, so you need to learn what your own is like so that you can truly know what you are allowed. So compare with a sat nav if possible, or other bikes if they have been able to asses how accurate theirs are.
Of course speed limits are a limit and not a target and they do not need to be achieved unless conditions allow, but if conditions do allow, then yes as an advanced rider, you will be expected to demonstrate that you are capable of riding up to the speed limits, and that will generally mean you need to make progress.
If you cross the line (wherever that line is) and start riding aggressively then I wouldn't expect you to pass the IAM test while doing so.
HTH or let me know
