Many thanks for the compliment about my graphing but the praise really deserves to go to @David for giving me the tools. I did use Today’s Plan for a while as that looked a bit prettier (lots more money) & also allowed me to have a different dashboard for each discipline & then a combined overall one. But I switched when I worked out that Intervals sort of does the same by selecting & deselecting which graphs to display. Plus I can customise the graphs.
I do feel as though HR seems the better determinant for effort level with my swimming as the screenshot below illustrates. The swims felt very different in terms of effort, one quite fast (for me at least) but the other gassed at the end! Pace based load has them almost the same but HR based load recognised the marked difference between them. The 30s difference in time seems small (less than 1 sec per length) but represents a big step up in effort.
I am a relatively poor swimmer in that my front end is reasonable efficient (though weak strength), my breathing good (though mostly unilateral) but my kicking & body position is poor.
As an aside, one irritant was my watch recording only 999m which means that it is not registering on the Interval pace chart for 1K. My vanity says that it is worth the effort of using Fitfiletools as it was a 1K PB but it is a pain. It is not the first time that it has happened. Why does Garmin think that I would stopped 1m short? Sensible software would surely have rounded up!