what waterline length…
depends on the weight in the boat. Many often give a suggested weight range which will put the waterline where its shape gives the best performance. If your weight without camping gear is at the low end and with gear at the high end then one boat may work well or if you have enough $$$ you get one each that fits best those two weights.
Will never happen. They would sell fewer
boats if they defined who they are for. Also, body shape, weight distribution, skill level, personal preferences, water conditions, all make a boat perfect in one instance and a nightmare in another. We have to use each others boats to get a sense for which ones might be fun for our next one. 
Bill
head-desk
No really, this is informative.
But I can see the thinking behind this thread spawning a whole lot more boats around here.
Good thoughts on this thread
Another twist is what may be great for a “rolling” playboat may be all wrong for a “rock gardening” play boat.
Manufacturers often refrain from capacity numbers as these are subjective and it gets folk thinking only in terms of some numbers Vs actual performance for them. Better to have a discussion about needs, styles, etc.
As in this difference?
“Another twist is what may be great for a “rolling” playboat may be all wrong for a “rock gardening” play boat.”
Perhaps a boat with a low and shallow stability curve for rolling and a steep and high stability curve for rock gardening? The first tender, but easy to get back up; while the second would be harder to knock over, but more effort to get back up?
More Manueverable
On a windy day it’s much easier to manuever a kayak that’s sitting lower in the water.
Lower volume feels great. Instead of paddling the boat you feel like the boat is a part of you.
Numbers/dimensions
While I have to admit going through phases of charting statistics on kayaks, the numbers do not give most paddlers a full sense of the personality of the boat.
A designer may know how all the available measures interact creating the personality of a boat - but most of us can only get a very rough idea from pouring over the stats.
My understanding is that even after all the calculations are made and the prototype produced, it takes actual paddling in an array of conditions to hone the personality of a boat.
Most of us rely on anecdotal information from other paddlers, maybe combined with some stats, to determine which boats to try in order to find ones that suit our desires.
Fortunately, playing in boats is fun and most paddlers enjoy having someone else try their boats 
or more marketing hype
Paddling other folks boats.
I like that! My problem is, there are not many people around these parts that have boats I really wish to paddle. Occasionally there is a demo day that include some, but not often enough. You, Wilsoj2, seem to have a rather full aray of boats I lust for! Where do you live? Just kidding, but you get the point! Ken…
somehow I maged to squeeze
myself in my girlfriends Nordkapp LV but it was not pretty
I was plowing in the water and needed help to get out of the boat(it was like uncorking me).
My legs are a little bit on the large side from all those years of hiking and cycling.
I guess I am not the norm…
Northeast
We traveled a couple/few hundred miles around the Northeast when we were trying boats 6-8 years ago. Now there seem to be a good array of boats within easy reach.
When we got our first Brit boats, we were pretty much the only such owners in our extended paddling group. These days when we paddle most or all of the boats in the pod are British.
CD goes Brit
Current Designs, with the non-Brit Caribou as its more popular long touring boat, now introduces 2 new Brit style boats. Interesting.