That was a very helpful write-up, thank you! I actually follow most of the points you've outlined, but I'll highlight what I do differently.
Ingredients
1. Interesting enough, I've been using higher protein flour, since the main recipe that I've adapted along with other sources I've read recommend doing so. To add on to your next point about the mineral water, the recipe that I've used my main reference (
here if you're interested) is also on the low end of hydration, using 150% water/eggs, so it's odd to me that formula still works well for him. It makes sense that a drier dough cracks more. My choux paste is indeed drier than others that I've seen, but I did that purposely to avoid adding more moisture that would lead to more expansion, and hence cracking in the oven. I live in Canada, so our flours here are a bit different. Our AP flour is around 13% protein, and we have another product called "Cake & Pastry Flour" that's around 7-8% protein and is chlorinated (essentially American cake flour). Next batch I make, I'll try a blend, like I've been doing with most pastry doughs, to achieve a lower protein content.
Mixing
8. I've been cooking the panade to 170°F, but I'll admit it sometimes gets over as it takes my thermometer some time to get the correct reading.
12/13. As I've mentioned above, my paste is a bit drier, so it's not very glossy and doesn't make as much of a "V" when hanging off a spatula. Using a lower protein flour blend should make it pass those tests better without necessarily having to increase the hydration.
Baking
1. I like that you mentioned the Ateco #868 tip, since I actually bought that tip specifically for eclairs! I concur that it produces better results, as there was a noticeable difference between using it and even a regular open-star tip.
2. I'll include tests using a pan of water on the bottom rack in the future too, but don't want to change too many variables at a single time.
3. I've seen others recommend Silpat mats for eclairs (and of course there was the Chef Scott Green video showcasing Silpat vs. Silpain), but also as you've said previously in this thread, they are a bit niche in their uses. However as I get more and more into baking, it may be an investment that I'll make in the future.
And also reviewing my pictures, I'll admit that the shells could have been darker. I baked at 350°F for 40 minutes, but next time I'll try 45 minutes or even longer.