Current limits lack credibility. They are frequently ignored and modern cars are capable of cruising safely at speeds well in excess of them. Speeding is not a factor in more than a small minority of accidents.
Before the 'road safety' lobby become too enraged, it is not unreasonable to expect that a driver concentrating closely driving at a speed at which s/he feels comfortable is likley to be be driving with considerably more care and attention than one who is driving along at a lower speed than s/he really feels is appropriate and whose mind is more likely to wander. This particularly applies motorway driving, where monotony and a lack of changing circumstances can result in there being little in the way of external stimuli to maintain concentration.