OS X nudges past Linux for me because it is much more efficient (this is what I was alluding to in my statement about hardware and software working together). If Linux could work out some way of being just as efficient with the battery as OS X, I would put Linux on my laptop instead of keeping it only on my server.
I don't know of any objective benchmarks on that regard, but I do know that Linux is famously erratic in conserving power, with results often varying a lot depending on the specific hardware.
