Over the years, I have commuted on various old steel road bikes, ranging from a 17kg 1973 Schwinn Varsity with aluminum wheels (huge improvement!) to my 11kg 1959 Capo and 1980 Peugeot PKN-10. The Varsity was indeed bulletproof and theft-resistant, but I really noticed the weight during my daily 12-percent climb and when trying to accelerate or to sprint out-of-saddle. (A frame that heavy is not "tossable.") For commuting, I like the Capo's ample mudguard clearance and comfortable ride, but it does get squirrelly when I load the rear rack even moderately. The Peugeot, with its 100cm wheelbase and beefier stays, is a good all-round commuter, as was my humble old Peugeot UO-8, before I cracked a chainstay.
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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