: After a winter season of racing surfskis here in SoCal, I'm just a
: bit shocked! I hadn’t tried my Black Skimmer sea kayak design
: with a wing paddle, so for my workout this evening, I thought
: I’d give it a go. Despite the Black Skimmer being rudderless
: and skegless, I matched my surfski times on the coast.

All other things being equal, a properly designed surfski (ex. Epic, Fenn etc.) will always be faster than greenland-like s&g boat with wider beam and shorter waterline.
Since hydro-statics do not lie, the reason must be something else. How was the average speed measured? Are you comparing apples to apples?
If so, then the only thing left is the paddler. Surfski (similar to K1) is quite unstable, and requires excellent balance to apply the full power. It's much easier to apply full power in the boat you designed, built and are intimately familiar with than in the tippy surfski you are just learning to paddle.
This does not negate the main point - you may go faster (today) in your S&g boat, but you will always (at least theoretically) be able to go faster in surfski.