Terry, what I think is really interesting about your version of my 500 set is the "fact finding" nature of it. In your case, you had no trouble completing the first 500 at 1.3sec/stroke...but then you used that as information to guide your next set. (I can do it better...)
And as a whole you use the entire grouping of 5 x 500 to collect information and help you guide your future work in the 500 arena (identifying the inflection point as you called it).
I suppose that depending on where someone is in their swimming practice, experience, neuro-muscular imprinting of good stroke habits and general fitness (is this the least important?) the same set of 500 @ 1.3 seconds will have a variety of outcomes, leading to an infinite possibility of future sets...and innumerable learning outcomes.
I'd love to hear the results of others who try a similar set...how & why did the choose their starting tempo, were there stroke counts as expected, where do they see room for improvement, and how did their NEXT WORKOUT go in comparison to the first?
i think that's what's the most interesting to me personally, is seeing my own evolution of this effort over 3 workouts in a period of 3 weeks...there's no way I gained that much aerobic fitness to go from not being able to complete a 500 to breaking my PR twice in 2 weeks. Yet I still see room for improvement at 1.3 sec/stroke (the last 200 was a bit wonky), and I have lots of time to work on the 500 set at faster rates as well.
Likewise, what if I slowed my tempo a bit? How slow is too slow if it allows me to swim even further? What stroke count is too high for a longer set like this? I'm striving for 16 SPL, yet your sets also encounter SPLs of 16 (albiet at a 23% faster stroke rate), and you're 8" taller than me...what if I let my SPL go up to 18-20 as a starting point? What tempo can I swim at the faster rate? Hmmm....the simple process of answering these questions requires a lot of trips to the pool. How fun is that?
From a coaching perpective, how do you create workouts like this for someone else to follow without first allowing them to spend the time they need learning how their body responds to paced swimming, or learning how to modulate stroke counting? It boggles my mind sometimes. (more often than not!)