I didn't read all the posts in the thread (I'm kinda lazy) ... so this might be repeating earlier posts:
Not all rail-trail 'gravel' is the same, so tires that work on 'your' rail-trail might not work on 'their' rail-trail.
That said, Frau Toad spent many years riding & miles our local rail-trail (Lake Minnetonka Trail) with a crushed limestone surface on 23 to 28 mm road tires without a single complaint. I've find 28 mm T-Serv tires great on any rail-trail surface I've seen around the Twin Cities. Frankly, rail-trails are straight and flat so there's very little need to worry about handling/grip.
I should point out that I'm also the Toad that'll ride 4" fat tires on these same trails ... So there's that
