It obviously depends on the individual person, but I've trained with two guys who both ran sub 1:05 and both of them ran 100+ mpw. One was a reasonably successful D1 runner and the other ran the marathon in the World Championships a little less than a decade ago (for a different country, not the USA).
I know I couldn't break 70 minutes unless I was running 75-85 mpw but to be honest I'd rather run the 3000/5000 on 60 mpw. Much more fun (and more "fast running" in relative terms).