If you were going to do a lot of brevetes on rough gravel roads, I’d say, “Go for it!” I think my sig contains a link (can’t see it on mobile) to my ‘83 Stumpy. It’s mostly original but for the tires, fenders and crankset. I love riding it on gravel and don’t feel sluggish on it. I have ergonomic grips on it now which have vastly improved hand comfort when spending hours in the saddle. So far my longest ride is about 35 miles, but front loaded for light touring and probably four hours over rough terrain for much of it.

For road riding, I found 650x38 tires to be just great. 42’s would handle county gravel roads even better, but the 38’s get by most maintained gravel roads just fine.

If if I had a bike that only fit 30mm tires and fenders, I’d look into the feasibility of a 650b conversion...

As for stock 26” wheel Rando bikes: VO has been mentioned, FMBxEndpoint Hunter/Gatherer, and the ones I desperately want, Elephant NFE or Crust Romanceur.