My opinion is the size of the daggerboard is not very important, in other words a really big daggerboard does nothing to help you. The whole key to kayak sailing is 'forward motion', basically the boat needs to be moving forward for the rudder/daggerboard to function (ie...water flowing over them). Basically if the boat is going 1 mph thru the water, neither do much of anything. Because kayaks are tippy and difficult to counterbalance (with your weight), they must always have smaller sails than what a regular sailboat like a sunfish or laser would have. In other words if your out there trying to pretend your a sunfish, your defeated and not using the kayak sail for it's intended purpose, your much better off just going out and buy a sunfish or Laser ( I used to have a sunfish).
All Hobie mirage kayaks are designed from the ground up to utilize the mirage drive system and the Hobie kayak sail kit, (basically designed from scratch as a pretty good little sail boat, (think about it all Hobie's employees are sailers first.....). If you take the mirage drive out of the equation you are left with a pretty crappy paddle kayak (all Hobie kayaks except the TI track terribly when compared to even low end paddle yaks), whats the point in doing that (lol).
Same applies with the Hobie sail kit, if you omit the mirage drive out of the equation, the Hobie kayak with the sail kit (less the mirage drive) is even less capable than a standard paddle kayak with an aftermarket sail kit, (which is pretty much the most useless thing you can possibly do on any paddle kayak, (a gigantic waste of time and money)). If you wanta sail get a dang sail boat.
We have had many different Hobie Mirage kayaks and are out on them most weekends since moving to Florida ten yrs ago. We have never taken a Hobie kayak out onto any water without a sail kit strapped to the side of the boat (not even once). I had a sunfish sailboat and never took it more than 1/2 mile from shore and all we ever did with it was zig zag back and forth in the wind, and try to sail around bouys (pretty darn boring). Kayaks are a totally different world, you actually go out and do things with them, go to fun destinations, and really see and enjoy the natural beauty up close and personal, and can explore to your hearts content (not just a postage stamp sized 1/2 mile area). We have well over 200,000 road miles with our camper in tow and kayaks on the roof, and have dropped into every body of water that we could find, all over the country (even mild rapids). One of our favorite things is to kayak up rivers with our favorite place being the Sante Fe river (just north or us) and visit all the natural springs (13 springs in an 8-10 mile stretch). We still have our sail kits strapped to the side of the boats, but get little wind in all those trees, listening to all the crazy monkeys left over from the old Tarzan TV series from the 50's.
When we first started kayaking we were renting paddle kayaks and never wandered more than a few hundred feet from shore, and seldom went more than a mile or two (gets boring fast). Once we started using Hobie Mirage kayaks with the sail kits we were able to easily quadruple our range, and felt safe going much further out (even into open ocean). Our main pastime is snorkeling and diving, we get to do that all the time with our Hobies. If you ever snorkel around here you will quickly discover every body of land is surrounded by totally bare lifeless shallow sand with water only a foot or two deep, pretty hard to dive in knee deep water. We don't fish at all, but do a lot of spear fishing where we can select from the menu (lol). Just FYI I have never seen anyone fishing from a sunfish or laser, or seen one more than a mile or two from launch.
Both my wife and I can peddle our Hobies for up to 10 hrs if needed, adding the sail kit lessens the physical requirements tremendously, when usable wind is available. We still pedal 100% of the time even with the sail kit deployed, but can peddle at a much lower pace (walking pace) and still get where we want to go in decent time.
The whole key to kayak sailing (especially upwind) is to try to keep your forward motion up via peddling using the sail as a power assist,(not your primary propulsion), the sail is too small to do anything else, and there is no practical way to install a larger sail because of balance issues.
Don't try to pretend your a sail boat, what you have is way better.....
All just my opinions
FE
Just a few of our crazy kayak sailing setups...
Our old Oasis
One of our two matching (his and hers) Revos
one of our TI kayaks rigged for kayak sailing with a wing sail.
One of our TI's all rigged for far offshore.
Yet another one of our TI's at Lake Hartwell GA last summer, (thats our new camper in the background), lake hartwell is 45 miles long, we covered quite a bit of the lake. In both sailing mode and kayak mode....
We love our Hobies (lol)