I'm a 15.55 5k runner that tops out at 50mpw solely because of injury at above that. id say my average pace is 7min miles. 6.45 when fresh and more like 7.15/7.20 the day after sessions or when tired. I actually feel i would get injured running mileage at 8min miles as i start to hell strike badly at slow pace. Everyones different i know people that run all their mileage quicker than 5.45 doing 100 mile weeks and they are the same standard as other people that run their mileage at 6.30-7. All relative to yourself. Do what keeps you from getting injured and improving rather than trying to do what other people do to get success.