Race Segment Improvement Question

I have another question:

When I run the speed endurance workout with incomplete recoveries, say, 4x60m 4x60 with 20m intensity limit as per short to long, how do I know when it’s time to stop the workout all together being that I run these with incomplete recovery’s?

Also, do I try and run up to the proscribed limit at 95%+ even though I feel fatigued? So for example, a workout of 4x60, 4x60 with 20 meter intensity limit do I basically run all the 20m runs at 95%?!