Under 7 minute pace is the golden pace at which one can improve. 8 minute pace is way too slow and does not require the mechanics needed to run a 4:30 mile. Therefore, you develop bad running form habits at 8 minute pace (which translate into a slower mile time)! Not only that, but there are no practical gains to be had by running that slow. If you can't run under 8 minute pace, you should either hit the track to gain basic endurance (building up the distance from a shorter one to a longer one) or take the whole day off.
You can not be a champion if you run the majority of your miles at 8 minute pace. You can only be an average runner. To be great, you first have to make sure that you're able to run somewhere in the 7 minute pace range for up to 5 miles. Then, you drop your easy pace down to 6:30. If you don't believe me, there are many Wesfly or TheAthleteSpecial episodes where they describe sub 7 as "easy".
Once your easy pace is 6:30, you can advance to increasing mileage up to 10 instead of 5. But in doing this, your pace will decrease to the 7s again. That is okay, but you must start the process again of improving your easy pace down to 6:30.
The only way this strategy works is if you supplement with weekly repeats. Like 400 or 800s, for example. That is a main component, because those repeats give you the "muscle memory" needed to run fast. If you have ever jogged the day after doing these, you would know what I am talking about. You don't even have to think about running with the "correct" form, because it just comes naturally.
Weight lifting also helps neuromuscular coordination along with the sheer POWER needed to run fast. Ever watch the sprinters at meets? The best ones have very lean muscle, and distance runners need the same to some degree.
By training yourself to run a faster easy pace, you give yourself the ability to train your threshold with higher frequency. Your threshold is the most important tool required to run fast.