What Ya Tu Sabes says is technically true since the wear is spread over more teeth. For practical purposes I don't even take that into consideration. I try to work with whatever I have in the parts box or whatever requires the fewest other changes. Chains, chainrings, and cogs are expendables anyway. I don't waste too many brain cells trying to make something last a few hundred more miles. Heck, I'm usually playing with things and changing them out long before they wear out.