Increasing speed limits to reflect the prevailing traffic speeds has long since been found to increase the speeds of most of the slowest traffic (the people blindly adhering to the posted number) and and reduce the amount of passing, lane changing and other interactions thereby increasing safety.

Basically the more homogeneous in speed and behavior the traffic is the safer it is.

You should be able to Google up some civil engineering studies at will. This stuff was "new" decades ago.