The other thing a headwind like that does is whip up a relentless sea. I reckon there were consistent waves of up to 1m, about 3 seconds apart, constantly bashing into my bow, further hampering forward progress. All of this action does to tend to focus your concentration however, & when I checked my watch expecting 20 minutes to have elapsed, it was actually near enough to an hour. I figured I would paddle a further 10 minutes (to a grand total of 3km in total), then turn around. The 3km or so that had taken me 85 minutes to cover into the headwind, took a total of 13 minutes on the way back, as I flew along surfing the short-sharp wind waves which had so hampered my forward progress.
The lesson for me was one about forward progress once things get towards 30knots. Basically forget it.