Thanks for replies, Matt, Wouter.

Matt, I have both "The Principles of Yach Design" & "the Elements of Boat Strength" sitting on my bookshelf, with the time to read neither. Hopefully I`ll get round to it some day soon as I have a genuine interest in the subject.
At the same time I`m trying to learn 3d Studio Max for architecture, just trying to keep up with technology in your own line of work these days is quite challenging.

So me asking the question is kinda like "guys, please give me a shorcut here, I don`t have time to study Naval Architecture for 4 years, just so I can figure out what the best solution is for daggerboard shapes."
Keen to build my own foils, but I`m not the type to just settle for what is "the done thing". Sure, NACA foil sections are tried & tested & operate over a broad range of conditions, but it seems that newer theories are challenging the old ones, have a look at wave-piercing hulls vs very rounded bouyant ones, a few years ago everyone would have laughed at the F18HT / A-class designs. Then there`s the unirig vs sloop debate, still open for discussion. No one theory is always going to win out over another, one may be better suited to a certain set of conditions than another.
When sailing against the Hobie Tiger, we are very close in speed upwind, but they can outpoint us by a large margin. Probably a combination of high-aspect rig, longer waterline & the Looooong daggerboards. Now, out of those three I can change the daggerboards up to a longer set with the least cost, I accept that it won`t be a major improvement as if I could change all 3, but I`m hoping for a gain of some sort. The best scenario would be for me to build a set of blades that are the same length as my current ones as they would still fit class rules, but gain in their efficiency as much as possible, hence the questions on how to "fine-tune" the design.
I`m well aware that higher aspect ratio foils / wings have a higher L/D ratio than low aspect, paragliding taught me that. It also taught me that flying a high-aspect ratio wing was far more prone to finding stall point much sooner than my old training glider, and was far more twitchy (thats what makes it more fun to fly .
I haven`t heard of any Hobie Tiger sailors pulling boards halfway up going upwind, even when it`s howling, maybe that problem is specific to a certain hull shape / sailplan, these factors always have to be considered.
Our class rules state max. daggerboard length = 1200mm, max. width = 300mm, giving quite a short square foil below the surface. Making the tip elliptical would increase efficiency, but substantially decrease the lift-producing surface area of the board. Where do you draw the line ?

So my questions are still open, and I`ve added another one !
Cheers
Steve