I paddled my Seda Ikkuma inside the bay, at about 4 kts, in a steady 10 kt cross wind and very light chop. The Ikkuma weather cocks very slightly, as a good design should, and is easy to control directionally with slight leans and slight sweeps.
However, my GPS indicated an increase in speed of 0.1 to 0.2 kts was achieved by deploying the skeg. Without the skeg slight sweeps and leans are required every 4 or 5 strokes, while with the skeg deployed even slighter corrections are required every 20 or 30 strokes. I repeated these skeg up and down trials multiple times with the same results.
The Ikkuma skeg is small, with high aspect ratio, but quite effective. Any drag increase due to the skeg is overwhelmed by the benefit of greater stroke efficiency.
YMMV. Don't know if this applies to any boat and skeg.