Update.
I rode 200K on the Ergon SM (Small/Medium) today. I didn't have much time to tweak angle and setback, as I just picked it up Wednesday. I set it up level, and tried to match the sit-bone location from my Sella. Sit-bone pain was definitely there; at 25 miles it was getting uncomfortable. From there on, I was out of the saddle on climbs or coasting down the steeper grades, just to get a break. I did some pulls in the wind, and found myself on the nose. I'd like to try the wider version, but the shop didn't have one in their loaner program.
Specialized Romin 150mm: No, too narrow. Consider the 158mm version.
Specialized Power 168mm: Maybe. Consider for a longer test.
Fizik Tempo Argo 160mm: No. Sit bone area pain 35 miles into 200k.
(pause in test, rode two 200k brevets on my Selle Anatomica. Which reminded me this is not the right saddle for me)
WTB Koda 145mm test. Very short test as I got sick mid-week. Maybe too short. The Ergon is similar so I'll do that next...
Ergon SM sit-bone pain at 25 miles. Maybe try wider version.