I'm comfortable driving a lot of highways faster than the posted limited, i choose not to most of the time because of the ticket risk and financial impact that it can bring. 10-15 over is generally accepted as not ticketable and I'll often set the cruise if equipped around that speed to prevent getting a ticket. There are others like me who will be going faster now by using their cruise or self control to maintain their speed.

Average speeds may not have changed much, that is far more to do with poor enfrocement than it is with the limit itself. Design is a factor but harder to narrow down for a highway like it would for a city street trying to calm speeds. A highway has to accomadate a 20 year old sedan, a large transport, a modern sports car, and a pickup truck at high speeds. Making it safe for the transport to maintain 110 is going to make it feel safer to go a lot faster in a sports car or modern SUV.