I rode D2R2 on a touring bike in 2010 with Dave Wages and a friend of his, and pretty early into the ride it was obvious that I had too much bike for such an event. So afterward I talked to Dave about building something with all of the conveniences of a road group, specifically Di2 with DA road brake calipers; he suggested XL tubes, a stretched chainstays, more BB drop and a bit of extra trail. I requested clearance for a 28mm tire, maximum, and couplers.
The Parigi-Roubaixs I have mounted measure close to 30mm, and with the pads at their maximum reach in the caliper slots, there's still
plenty of clearance. The bike rides pretty much like a normal road bike, but the longer stays, slacker HTA and added rake make it feel bigger and more stable. I am happy that I don't have weird gearing or (especially) cantilever brakes. Even in the **** DA brakes are fine.
If I were looking to have another mixed surfaces road bike built, I'd look to those builders who like to ride those kinds of roads and make a habit of doing it. Dave Wages, who participates in multiple gravel road centuries every year, Dave Kirk (do they even have pavement in Montana?) and Carl Strong, who has been building his "dirt road bikes" for years and years--those are a few of the best.
Chris--
Oh, and 'cross bikes are for racing.
