Interestingly, you'll fail your UK motorcycle test if you don't largely treat the speed limit as a target.

If you stick at 40mph or thereabouts going into a 50mph zone, the examiner may think you haven't seen the speed limit change. More importantly, if you don't keep up a good pace on a clear country road with good visibility where the speed limit is 60mph, they won't have confidence in your riding at higher speeds, and they know - as all bikers know - that you will almost certainly spend a good chunk of your riding career at higher speeds on country roads.