Ran 12x400 today with 90s of rest between each one and a 3 minute break after 6 reps. Not sure what the exact splits were, but I averaged about 75 and ran the last few reps faster than that (the last one was 70 I think). I felt relaxed throughout and didn't feel like I was straining to hold the pace until the last 400. What could I run for the 1600/mile right now? I'm running about 55-60 mpw.