Another update. I needed a new rear tire and this time decided that I'd go with fatter tires to go along with the Shockstop stem. I was able to squeeze a 700x28 in the front and a 700x25 in the rear. I pumped them to 95 today, as a first try. The ride was definitely more comfortable, way more. I stubbornly refused to try fat tires for 30 years, and now I don't know why.

My bike now feels like the Spec Roubaix I rented in SF that started me on this.