Back in 2009, when I was 51, I was gunning for my over-50 PR in a half marathon. Training had gone exceptionally well. I was an occasional participant on Tinman's forum, and when I posed a question to the general membership about what my recent workouts suggested I should do in the final two weeks and what my race strategy should be, Tinman gave me some free advice.
He told me to run progressive tempos in the next to last week--I may even have run them twice that week--in which I ran 3x2 miles with the fist mile somewhere between marathon pace and half marathon pace and the second mile at 10K pace.
As for the race: my marathon HR, my 85% of max HR, was 170. He told me to run the first three miles at a HR of 171-174, then slowly crank it down.
I ran 1:31 low. I averaged 7:20 pace for the first three miles, ran just under 7:00 pace for the next seven miles, and ran 6:52s for the last three miles. Just hammering. It turned into the perfect race. (I averaged 6:57 pace overall and it was indeed a PR.)