The efficiency drops with cog size, particularly quickly at the small size end, if anyone cares, as the pull force from a chain link is more and more misaligned with the usable pull force for the next link. This ties to the wear as more and more work is done by the leading tooth that wears at an accelerated rate.
That makes sense. It would be interesting to know approximately by how much efficiency decreases / rate of wear increases as the cog size decreases. Do you know of any studies or research? It could be significant (or maybe not) in real world use.
Edit: I guess I'll find out for myself soon enough. I have a Bailout cassette winging its way to me as I type!