Not trying to high jack the thread, but I'm interested in the same question (but for me).
I'm 61 and have run since 2015, doing several HM and a couple of 70.3 tris. Since I finally have some base endurance, I'm getting faster - but I'm still slow.
I've looked at several race pace calculators and they're all over the place. My race is next Saturday. I've been on a 12 week, 6-day workout plan that I like and have seen progress. I started the plan after one weeks rest from a 12 week
6-day work 70.3 plan and race. My goal pace is 10:30/mi and this is an "A" race goal. In other words, I'll spend the whole race saying - "This is a RACE". Some calculators say I can't run an 11' HM pace and some say I should be able to run 10:10 to 10:15 pace.
I'm into tapering now, but my last three long runs were 8 miles at 12/mi followed by 2.5 miles at 10:30/mi. My Monday runs generally included a single increasing time interval at 10:30, with this past Monday at 39 mins. My speed sessions are generally on Thursday and yesterday was "typical" with 5x3'@9:05+2:30'@13:30. None of these seem hard, like I can't complete the workout. I feel like I think I'm supposed to after them. The long runs and Monday runs feel pretty easy and the speed workouts feel like RPE 8/9 on the last interval (hard, but I could do another or more if I had to).
My last 30' TT I went out too fast (9;45) and slowed at the end with a 10:03 average pace. My LT HR is reportedly (from previous workouts) is @152 and my resting HR is 51. Garmin says my VO2Max is 41 (which doesn't help too much on an HM, but just another data point).
In 2020 (last time this event was held) I ran a 10:55 pace with a slowly increasing negative split (35:11 first 5k, 34:59 second, 33:15 third and 32:32 for the fourth, with a 6:30 for the last 1k. I focused hard on a negative split because I had blown up so many previous HMs.
I don't want to blow up this time either. I'm not confident enough about the 10:30 because of the calculators that say I can't even do 11/mi. My initial thought was to do like I did in 2020, starting at 10:45/mi and picking up the pace as I go. But I know I'd be fastest with a single pace throughout - as long as that pace doesn't cause me to blow up.
Anyone have suggestions?