There are probably no benchmarks yet, but from my experience (I use both 10.8 and 10.9 regularly) Mavericks does a better job on battery than Mountain Lion, wit

There are probably no benchmarks yet, but from my experience (I use both 10.8 and 10.9 regularly) Mavericks does a better job on battery than Mountain Lion, with about 1 hour of usage added. This is on 2012, 13" Air. The 2013 model will probably see even better gains.