I like what
@Al Ciampa said, and that's how I look at it. My goal is to be able to repeat some of these early training session - my event will be in the Fall or Winter - later on and see a lower heart rate.
But what
@vegpedlr said has merit as an approach, too - keep the effort the same but be able to do more.
I think it's also worth mentioning that there are "newbie gains" to be had here - the last time I trained for this event was five years ago, and I feel like I'm making rapid progress now as I get into doing this. I fully expect that my rapid progress won't continue in this way but I'm enjoying things right now. E.g., today I walked 5.7 miles - I haven't walked more than 3 miles in years, maybe decades, maybe a few decades. I felt fine during the walk, I feel fine now, and I'm planning on a strength training session tomorrow.
This idea that strength helps everything - I'm a big fan. My subjective impression of my current training is that it's going well because I am pretty strong compared to what I'd be if I hadn't been doing all this deadlifting and one-arm pushup-ing and work on the rings and whatnot.
-S-