A study one time said probably 80% of drivers overestimate their skill. Hopefully us riders are more realistic but I would not be surprised if it's higher. Truthfully, how many of you regularly go back to the parking lot and do the box, or practice panic stops? I know I don't and should.
So given the fact that most of us are probably egotistic and think we're better riders, in real life, backing it off to 7/10ths is probably a good idea to buy us that safety margin we'll no doubt need.