My first no-brainer change is put a prior-gen Dura Ace 11-23 cassette on the bike. If you are averaging 27, then you are spending most of your time on the small few cogs. The smaller cassette will give you single-spacing through all the gears you will commonly use and make it easier to maintain efficient cadence.

If you were going to make a chainring change, then I would jump to something like a 56. That would let you run more toward the center of the cassette with cogs that are slightly less drag than the little ones (less change articulation).