The problem for experienced drivers is that the setting of speed limits is very arbitrary and does not always tie in with the actual road conditions. Illogical limits reduce the respect drivers have for them as a whole with the result that many tend to treat them as a guide rather than a limit, which may or may not be helpful.
As someone who used to drive around 35000 miles per annum in this country and abroad, mainly in Europe and the USA, I tend to drive to what I can see rather than a number on a pole and so far that has worked. I did have a road accident, but that was in February 1973 and I did get 3 points for 'speeding' at 11-30 pm in 1989 on a dual carriageway near Norwich. When working I used to cruise at 85 to 90, but that was before electronic enforcement really got going. In Germany I would regularly cruise to Koln at 125 mph to 130 mph (Porsche 911 and/or BMW 735) back in the '80's. I have actually legally driven at 140 mph on the M1.The last time I did this was the night before the 70 limit was introduced in 1965.
Speed does not kill. What kills is inappropriate driving and this can be failure to concentrate, misjudging the road surface, misjudging the severity of a corner, failure to know one's own personal limits, failure to do on-going risk assessment all the time, etc. It is virtually never, ever, due simply to driving at over the posted speed limit.
I senior police officer friend says that the theory is that a really capable driver will be safe at all times even if there were no speed limits at all as he/she would drive safely anyway.
The obsession with 'speed kills' is something generated by those who really have no knowledge of driver behaviour or vehicle dynamics.