A good pace is just what scotty said, unless you want to go to the olympics then they might just have more stringent guidelines. No political correctness there, just a Darwinian excercise in survival of the fittest.
But a 6 1/2 minute mile equates to just over 9 miles an hour. Understand that on the road you will go slower than the treadmill as you don't have the motion of the mill to assist you. So say.... 7 1/2 minutes a mile? You still won't be running after 1 hour 40. So there you have it. 1 hour and 40 minutes of excercise and you are done for the day
Unless they put a hill in the route that would give Sherpa Tensing heart failure but we file that eventuality under 'X factor'