I think you can go under 5:00 RIGHT NOW. Five isn't beyond you, especially when you're doing those 10 X 400s averaging 78 with a minute rest. My first mile time trial--as a high school sophomore in Utah way back in 1978--was 4:58, and I wasn't running any speedwork yet, just road runs. Once I started doing 400s (440s back then), in just two months my race progression went exactly like this: 4:58, 4:53, 4:48, 4:44, 4:41, 4:39, 4:37, and a big jump at the State meet (on BYU's fast blue track) to 4:32. EVERY race was a little bit faster. Leaps and bounds as the speedwork really kicked in. The progression was so quick that I thought it would just keep going all the way to 4:00, but of course things got exponentially more difficult once I got below 4:30 the following year. You just have to put four 75 400s together. It might sound too difficult to you right now, but you're ready to do 5:00 right now if your workout report is legit. I suggest adding some 600s for strength. Ladders are always a good change-up: 200, 400, 600, repeated three times, with the 200s run at or just below your target pace of a 5:00 mile. If you can't do the whole workout at 5:00 mile pace, try a little bit more rest between reps. Do that workout a couple of times a week, gradually lowering your interval (rest) times, and you WILL get your 5:00 mile. There are many good workouts for milers that will work just as well, and a lot of guys on this forum are very knowledgable. This is just one good example of the kind of workout that will get you there. I like it because it gives you variety rather than just the same boring, tedious 400s. I'd like to know, though: How fast can you run an all-out 400? How about your fastest 200? Basic speed means so much to a miler.