Love my 32mm GP5000s, wouldn't go any smaller, you're not going to be giving up any noticeable speed.
Ditto - I was doing a race training ride on my gravel bike last night. Ave speed about 25mph, sprints over 30, max sprints just under 40mph. No compaints riding my gravel bike with the lycra boys when I'm on the 32mm GP5000s.
Going smaller just increases the chance of rim strike. No benefit in that. Besides, I'm probably running 1/2 the pressure of some of those guys, and on our roads that is a definite advantage (I seem to see at least one of the group getting a flat every week).