So, while our OP apparently hasn't been back to the forum in a while, I'm happy to report that my Brooks carried me for 32 miles/50 km of pretty varied New England roads today, comfortably. And I don't wear padded shorts, either.
I'm a little embarrassed to admit that this represents a lifetime distance record for myself, and I'm, oh, right around 50 years past my training wheels I suppose. Just had no interest in longer rides at all when I was younger, the bike was strictly for commuting. So you may imagine that comfort in the saddle was my no. 1 concern planning today's trip. Turns out my knees start complaining long before that would become an issue, still dialing in saddle height. But the real problem today was that I foolishly trusted the 40+ year old spokes on the Dawes for this ride. Broke one (drive side rear, naturally) 20 miles into the trip and my wonderful wife came to rescue me with the Zizzo folder in the trunk. Swapped the Brooks over and kept going!