What do you have now -- 52-42 / 13-15-17-19-21-23? (That was stock on my Bianchi.)
Simply replacing a standard (non-ultra) 13-23 6-speed w/ a 13-26 7-speed (been there ... done that) will give you a noticeably lower bottom gear w/o compromising anything else. I ended up gearing my Bianchi 50-42 / 14-16-18-20-23-26, for a superb 1.5-step progression from 43.6 to 96, which meets my needs well. I kept the original derailleurs and could have kept the original crankset, which I replaced w/ a newer Ofmega/Bianchi crankset which can take a 38T inner ring, should I ever need to drop down another 10%.
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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