I often do a 20-mile trip on B-roads & through villages where the speed limits are 20, 30, 40, 50 and 60mph in various places. On two stretches there are speed cameras, and a few months back I got a warning letter for doing over 30 in a 30mph limit - don't know by how much, but I was lucky not to get a fine.
So I stick to the speed limits, even though IMO some are a bit daft - the 20mph is only relevant at school pick-up & drop-off really - but it's not for me to decide the law.
So why are there always cars - always BIG cars - right up my exhaust pipe trying to chivvy me up? It's SO stressful, why not just relax & go with the flow?