10x400 on 60 seconds rest is pretty aggressive as a mile race indicator. I'd be pretty surprised if I was able to run 61.5's for that workout and that's my current mile race pace.
This really just shows the weakness in 'indicator' workouts though. Different runners have different strengths, so you can't take a specific workout and say that's going to tell any given person what their potential is for a certain race. I might have trouble running 10x400 at mile pace but no issues running 4x400 at sub-mile race pace while someone else is going to do the opposite.