Ecce you have made some brilliant gains there. consistent miles is a big key so no injuries. The way you are going you will smash a 4 hour marathon before you know it.
i still sort of follow this. well for 3 runs a week I run at 73% of Max which is 8.25 min miles. The rest of the time I am on the fells as looking at doing the bob graham next year, and it is impossible to keep the heart rate down.