Eh, I pretty much use my small two with my big front and my big two with my small front and all of them with my middle (because I'm too lazy to double shift most of the time). So I can't say I use all the possible gears, but at one time or another I use all of the cogs.
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Bikes: 1996 Eddy Merckx Titanium EX, 1989/90 Colnago Super(issimo?) Piu(?), 1990 Concorde Aquila(hit by car while riding), others in build queue "when I get the time"