How vintage do you want? The famous and pricey Alex Singers and Rene Herses are probably still among the best models for high quality lightweight distance bikes.

My 1984 Trek 610 is pretty good, but I think it needs more low-speed stability. I also have a Woodrup Giro that has the same problem, but has excellent stability at cruising speed. It wants to go in a straight line when I'm tired and distracted. Both of these bikes have a tendency to shimmy when descending, the flexy Woodrup worse than the stiffer Trek. In contrast, a true road race bike like my Mondonico (early -80s) is not showing any of these characteristics. Which is better for long distance? I'm doing my century training on the Mondonico.

If you look in the Long Distance Cycling forum, you'll find a sticky on bikes for audax and other very long distance events. Those who actually do it are making choices over a wide range of bikes.

Road Fan