In a nutshell, the speed of this 25″ wide, 124″ long W kayak is comparable to that of 12′-13′ monohull kayaks, depending on their design: Fishing kayaks are normally much wider than other kayaks, and therefore slower.
This figure is the result of many tests we ran over the years, and many paddlers including amateurs, professionals and customers have confirmed it independently.
It’s important to remember that when comparing the speed of two boats you need to be proficient in paddling both of them. For example, it would be plain stupid to ask a canoeist who has never paddled a kayak before to evaluate the speed of a 20′ long racing kayak… Similarly, you don’t expect a sea kayaker to be able to appreciate the speed of a fast canoe if he or she has no canoing experience at all.
Therefore, before you try to check how fast your W kayak can go you have to spend the time necessary to become a proficient W paddler, and that can’t happen in a day since W canoing is somehow different from regular canoing, and W kayaking is very different from regular kayaking.
Expect the expectable: There’s a learning curve in this process, as there is one for any new activity you’re undertaking.
Note that the smaller the boat the harder it’s penalized for extra weight – Don’t overload your W kayak.
In case you want to join a group of experienced sea kayakers on a trip you should know that fast touring kayaks are narrow and usually over 16′ long, which means they are likely to go faster than your 10′ W.
This is a link to a long technical article on this subject: http://www.wavewalk.com/KAYAK_SPEED_ARTICLE.html