Today I ran a hard 5K just to evaluate how this 80-20 program is working. The last few hard workouts I've done has been either on a 10 lap indoor track or trail so splits are always slow.
I've run several 5K time trials on a straight bike trail with 3 small inclines- 1 in the first mile and 2 in the second mile. Today I tied my PR on this trail with negative splits.
I've been experimenting with a very slow pace on most training runs (9 min pace or slower) trying to conserve legs for the hard days while at the same time slowly extending longer runs (15 miles on Wed, 8 on Thursday). So far so good.