Originally Posted by Lucky-Charms
Of course all of this is pretty minute to begin with, but wouldn't a smaller ring/cog combo, while yeilding less engagement, be more efficient because of the smaller amount of friction from that smaller engagement? If you're only pulling on two teeth instead of four, you'd have half the surface friction.
I think that the friction difference will be essentially a neglible factor assuming that your chain is properly lubed. I think the main reason to run bigger is to try and reduce the stress that the chain has to deal with.