If chain and cassette life are primary concerns; use cassettes and chain rings with more teeth as [MENTION=450515]Eggman84[/MENTION] says. Consider 14 teeth for the smallest cassette cog, and make up the rest of the drive train to suit. Admittedly, this is a few grams heavier (cogs, chain rings, longer chain, possibly long cage RD), but it will last longer.