Must be the season. I've been thinking about this too. Last weekend I paddled my usual 10.3 Nmile run on Santa Monica Bay playing with a small metronome, GPS (& my 17' Great Auk).
I averaged 4 knots outbound, 3.5 home. Basically typical given my current conditioning, etc... Good conditions 3 foot swell. a little wind... The metronome helped a bit going against the incoming tide at the beginning. On the bay it was clear that stroke technique was critical. It was also clear that I don't usually paddle more than 5-10 minutes with the same stroke.
What's important however seems to be paddle technique and acceleration in the water. I was able to keep up (briefly) almost 5 knots with considerable effort, heart rate 140 bpm. After a few minutes rest I was then able to keep the same pace with a much lower effort and much lower heart rate. Clean entry and as rapid as possible short stroke with the cleanest possible exit seems to be ideal--at least for me.
To speed up my stroke I push forward with my off-stroke side pivoting on my power arm.
A lot of my excess and wasted exertion takes place at the end of my stroke. I calculated once in a six hour paddle with 3600 strokes an hour (cadence of 60 per minute) I had liftied 43000 lbs of water for no good reason.
Speaking with other paddles, outriggers, surf skis etc... if it's speed you want the surf skis seem to have the most advanced hulls, the outriggers are second and we kayakers lag behind..... (of course there are other important considerations for us to keep our 'yaks.) The best stroke also seems to be difficult to consistently execute because it's not 'even' like walking.

Anyway, that's my two cents.

Will