Your kind and helpful responses made the original thread long so I'm starting a new one.

Updates: the Maggy London dress was a no out of the gate. The fabric was clingy polyester knit, so dreadful for August I didn't even try on.

The Rag and Bone dress also failed, for being too short and too voluminous. You will recall I had already rejected the R&B as too casual for the wedding but thought I might keep for myself.

So the search goes on.