When I set out to buy a bike for audax rides up to 1200k, I had some criteria I felt were important for me. Tire clearance, stack, reach, type of brakes, bottle mounts, fender mounts, geometry. I looked at cx bikes for the tire clearance, but most lacked mounts and had aggressive geo. Case in point, my Focus Mares AL. Weirdly has rear fender mounts but zilch for the front fork. I've hacked on a front fender for commuter use, but that's not going on a 1200k. Too twitchy, too harsh, no good way to mount fender or lighting. Most road bikes didn't have tire clearance I wanted or stack I wanted. I bought a Soma Fog Cutter frameset, which is more or less a road bike with massive tire clearance, disc brakes, high stack and fender mounts. A disc fork with wide clearance, drilled crown and fender mounts not super common. Built up my auduax bike and it's been great. One 1200 on that bike.

Fast forward a few years, and everyone out there is marketing a bike with essentially the specs I wanted. Trek Domane. Hidden fender mounts, clearance for 35mm+, iso whatever frame. Rides smooth as silk. I finished 1200km PBP this year with a smile on my face. Literally; there's a finish line photo and I'm genuinely smiling, not grimacing. I don't care what they market it for, it's an audax bike for me.

Now people finish PBP on every type of bike known to man, including pre-war barn finds. One might argue the bike means nothing, or a 70's road bike is the pinnacle of bicycling perfection. Heck I dream of being like my buddy Ian and riding PBP on my fixie. But that will be hard AF, meanwhile my Domane was butter.