One of our staple workouts in college was 70-90, as in a lap in 70, a lap in 90. We'd usually do this for 4 miles total. I usually had to take an extra 400 very easy half way through. Our top guys could go the whole way and maybe do an extra mile or run more like 65-95.
Either way, it was 4-5 miles of running averaging 5:20 pace. I always felt like I could respond to moves in races no matter what the situation was after a few sessions of that workout. We did it a lot early season. Late season we might go 68-88 but only for 4000-4800m