I started with a 42/18 (63") and ride as high as 52/16 (88") on a good day.
For most rides or commutes I find a 42/16 (68") up to a 44/16 (74") works best.

My current herd and gearing:
Motobacane Mirage 52/16
Motobacane Nomade 52/18
Free Spirit 52/18
Miyata OneTen 52/19
Van Dessel Country Road Bob 44/16
Lotus Elan 52/20
Schwinn Le Tour 42/16