great questions. I kind of think the current TI thinking might be along these lines: do however much to lengthen your stroke that you can sustain for the pace and time you are aiming for.
There seem to be some ever-shifting priorities in my own practice:
1. Work to be as perfect as you can (my work with low SPL at slow speeds is an example)
2. Work to increase speed while maintaining you current level of perfection, both by maintaining SPL while increasing tempo, AND by decreasing SPL while maintaining tempo
3. Work to increase the distance you can swim while maintaining your current level of perfection
4. Practice at your current optimal performance level (i.e. the SR and SPL that will give you the best performance right now, even if that's not as perfect as you can be)
5. Work to increase awareness and focus
And one that's missing from your list, but I think might be the most important for me:
6. Work to use less effort for the same results
Not really an answer to your questions, I know. Are there answers, once and for all? I kind of think not.