I set my previous PR at 70ish and have run as high as 92 consistently. My PR is 4:12. I'm currently in awful shape and overweight. I ran 30 miles last week so I'm one week into it. I'm thinking of something like this as an 8-week crash course:
Monday: threshold intervals
Tuesday: E+sprints
Wednesday: Fartlek or VO2 max intervals
Thursday: E
Friday: Track 800-1,500 pace intervals
Saturday: LR
Sunday: off/30 min jog/XT