A 40+ female runner's journey to the sub 50 minute 10K

[Mistral]

Cycle #2, Day 3:

3x2K LHR AHR MHR
9:44 145 173 180
9:45 133 177 184
9:48 142 180 187

Unlike three weeks ago, today I managed to keep the pace through all three laps (I lost a few seconds on the last lap because of a careless cyclist, so it was even more regular than it looks). It was very warm (25°C) and it got pretty tough at the end, but I'm super pleased with the session.

What pace (or heart rate?) would you suggest I aim for on the Day 5 1hr45min long run?

Thanks!