The narrowest tires I own are 33’s. All in tubulars.

35’s are the narrowest clinchers I currently use. And that’s really only because my touring & townie bikes can’t fit wider with fenders. I guess that’s my default favorite width for pavement now. Could be the comfort and quality of Rene Herse tires and TPU tubes, but I don’t see any reason to go narrower.

27x1.25 is probably the narrowest I’ve ridden in the last decade.

I’m fully bought into Jan Heine’s writing on the subject in the “All Road Bike Revolution” book. Comfort can be fast. I placed in the top 10 in races last summer on 47’s. And I’m no seasoned race dawg either.