All right, I managed a 30-minute pool session in my usual 25m pool. My goal was to test my normal open water stroke for SPL and time.
I managed 14-15 SPL. I'd guess 15 SPL is right about my normal open water stroke, 14 was a slower SR. So I'm right where I predicted by feel, which was nice to see. Intuition and feel, for a trained swimmer (or any athlete, really) can be quite precise. I remember when I was running, I could guess my pace with a few seconds per mile consistently.
Speed was the inconclusive part. The pool was crowded, and I didn't have enough time to really test myself. But I think my default speed at 15 SPL is around :44/50m. I was able to swim :39-40/50m at 16-17 SPL.
I'd like more time to test the "downward drift of lead arm" against the patient lead arm style. Maybe that will happen later this summer.
Final conclusion: however different my stroke feels to me, it hasn't measurably changed much in the past two months. I plan to start adding pool sessions to my open water swimming in August when I am back in the Marshall Islands. Without pool sessions, I don't swim fast. And without swimming fast, I'm not going to get any faster.