I agree with nyloco (hi scott!) not be shy away from the faster intervals, but to use a different method of alternating between longer intervals and shorter intervals every other week.
I use this system:
Week 1: 2000-2400 repeats away from the track at 10k-15k effort.
Week 2: 800-1200 repeats on the track at 5k-8k effort
Week 3: 300-600 repeats on the track at 3k effort
Then start all over again. It allows you to work each energy system without trying to overload one system - as long as you have completed one of these workouts in 21 days, you are never too far away from the three energy systems you need to in top form.
I also would caution masters runners from getting carried away with JD pacing system in his books. I also would caution master's runners against having more than one really hard day in a week. Where I use to have 2 really hard days and a long run - it resembles more of 1 really hard day, 3 days recovery, one moderal day, rest, long run.
No more back to back stuff and no more of that carrying over fatique to the next hard workout or into the following week. easy means easy now.
just some stuff to think about.