I have two perspectives on this; one that, as others have said, the limit is just that and not a target.
Also, driving 'too fast' or 'too slow' in situations where the speed limit is being (almost largely) adhered to is subjective; for example, yesterday I was driving along a wide, clear 40mph limit road at about 41/42 mph and the bloke behind me clearly thought I was driving 'too slowly' (I know this because he tailgated me, flashed his lights, made hand gestures and then aggressively overtook me, making more hand gestures and flapping his gammon-like gob in what I assumed to be explicit swearing and name-calling).
Had I been driving at 30mph, he might have had a point, I suppose, but that's still no reason to act like a twat.
Then again, many of us drive more 'slowly' when we're not on a deadline, have some time to kill and are simply enjoying being out and about. I know I do. Sometimes, on empty country roads around where I live, with the roof of the car down, I'm doing two-thirds of the speed limit and enjoying myself. I might speed up a bit if a car appears behind me, but on country roads, I'm always going to be that little bit more careful.... not least because the chances over happening across a freshly-dumped pile of fly-tipping in my local area are pretty high and I'd rather not get a bedstead stuck in my grill or rip the sump off my car on a partially-dismantled shed.
In my oh-so humble, middle-aged view too many people drive 'too fast' and, more to the point, too bloody aggressively. It's a phenomenon to me why usually sane beings suddenly morph into some kind of teeth-gnashing, raging lunatics the second they get behind the wheel of a vehicle.
Mind you, I honestly believe that most things in life are enhanced by slowing them down - with the possible exception of the whole airport/flying anywhere experience.... roll on teleportation!
I've digressed, and waffled, apols.