My ca. 1960 Capos and ca. 1980 Bianchi certainly fit the scenario posed in this thread, and I concur that the evolving quality of roads was the principal driving factor. My Bianchi, relaxed by modern full-race standards, is about as stiff as I care to go.
I like the Capo for long leisurely roads, but I favor the Bianchi for climbing and sprinting.
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"Far and away the best prize that life offers is the chance to work hard at work worth doing." --Theodore Roosevelt
Capo: 1959 Modell Campagnolo, S/N 40324; 1960 Sieger (2), S/N 42624, 42597
Carlton: 1962 Franco Suisse, S/N K7911
Peugeot: 1970 UO-8, S/N 0010468
Bianchi: 1982 Campione d'Italia, S/N 1.M9914
Schwinn: 1988 Project KOM-10, S/N F804069