Obviously, I am not sure what will work, but I am very much enjoying trying things out. As this is my first season swimming in a decade, I have been taking things pretty slowly and trying to make my technique permanent over racing.
Originally I tried racing first, but I just could not do it without throwing away all my TI work as I described previously.
I spend most of my freestyle practice now (after a good stroke warmup) trying to maintain my slow SPL while swimming faster and I watch where my stroke breaks down. Hand entry is a huge weakness for me. So I will practice that more slowly at a low SPL, then after a 100, I try again.
I really need to start doing swim golf (where you add your time in seconds to your total SPL) to judge my efficiency at different rates of core rotation, but just swimming my practices slightly faster than normal has been yielding really good results for me so far. So I have stuck with it.