First, disregard your time from five years ago. It just doesn't tell you anything today.
The goal is to run an even pace. The best way to do that is run at a certain heart rate, not a certain pace, unless you are absolutely sure the pace is slow enough, i.e., that you can maintain it for 26 miles. I've tried it both ways (running at a heart rate and running at a pace), and running at a certain heart rate is the way to go for your first marathon (until you actually know what pace you can maintain for 26 miles).
I think 174 or even 170 bpm is too high. I think you will run out of gas. I would say keep your rate in the upper 150s or low 160s. I ran a 3:07 by keeping my heart rate at 158 for the first 18 miles, then letting the rate go up to maintain the pace. I felt great at the end, and ran the last miles exactly at the pace I started. In contrast, I ran another race at 3:03 a few months later, but my heart rate was 166-172, and I died at the end. Bottom line, the first race was very comfortable and the second was immensely more painful and difficult for almost no additional benefit. In the second race, I could have run the first 20 miles 10 seconds per mile slower and still finished in the same time assuming I didn't fade.
The biggest mistake marathoners make, in my opinion, is going out too fast. I've done that plenty of times and there is nothing more painful. The hard part is from 20 miles on. Running 5-15 seconds per mile faster in the first 20 miles is pointless if your pace slows by a matter of minutes at the end. That has happened to me several other times.
Take it easy for the first 18. If you still have gas in the tank, you will be able to maintain the pace or even speed up. Simply by maintaining your pace or speeding up, you will more than make up for the normal fade, which is a matter of minutes per mile for many.
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