I wouldn't factor chain life into the decision. The slight difference (if any) between wear of a 13-tooth and 14-tooth front, is much less than the wear of the chain due to usage. Repeated wheelies (which is the point of all of this gearing) is going to cause much faster wear on the chain as a matter of course anyway. I think going down 2 in front and up 3 or 4 in back is convenient because you can then likely stick with a standard length chain that you might already have. If you only go really large in back, you're committing to having to buy a new chain up front.
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