I had a good run this morning before work. I pushed myself and was able to do 4 miles at a 8:31 average pace. Heart rate according to my monitor peaked at 153, averaged 130.
My friend Ryan told me it is possible to push for a sustained mile pace of 6:00. He said that he used to be an 8:00 miler like me, but once on the treadmill tried to do splits at a higher speed. He said he ran 1 minute at a 6:00 per mile pace and discovered that he could go another minute. Then he pushed himself through several more minutes. He said it just comes down to how much you are willing to suffer. He now routinely runs at a 6:00 mile pace for 1-3 miles.
I would like to try to get to that level of fitness.