I guess all of your questions revolve around specific individuals and what they find important and what if any physical limitations they might have for whatever reason. Forgive the cut and paste below, but this is what I recently posted on a different board in regard to a similar question but the questioner was wondering about the differences between and S or D and the prior 25 Mac/Venture.............
==================================
Just a note, Ruth and I don't mind the smaller cabin of the S, but then again there are just the two of us. At home I show the cabin to someone and it seems so small. On the water it seems to get bigger the longer we are out. It would seem like it would be the other way around.
We don't even mind it that much with the pop-top down. Below we are sitting anyway and not walking around. If it is cold the smaller space definitely has advantages. We have our routines and seem to get along fine with the S and don't regret buying it.. I can see where some people would like a larger cabin though,
====================================
If you are 6'1" (I'm the same) you might find the V-berth on the 26 too short also. I did and that was the main reason for moving the head and moving the V-berth forward. It wasn't just the length, but the "V" and how it really crowds you in. After extending the V-berth we don't use the foot or so at the bow end except for storage, but now where my feet are there is some width. There is more width overall since we are now in a wider part of the boat.
Also now when using the john I can pull my pants up .
If you sleep aft, like most people do I don't think there is much comparison on the size of the aft berth between the 25 and 26.
====================================
With the pop-top up yes I can stand. With it down, no, but like I've mentioned before there isn't much reason to be walking around down below anyway. I can sit upright and my head clears the cabin top just fine.
The other day it was cold here and I worked on new wiring all day outside with the top down and it wasn't bad at all and often on the water we will have the top down at night if it is cold and will eat supper and breakfast and fix them with it down.
One thing to remember is that I'm 6'-1", but a fairly skinny yet 165 lbs, actually right now under 160 working on the boat so much, and I use to do a lot of caving when younger, so small tighter situations don't bother me so much. Ruth is 5'-2", but still can't stand with the top down either.
In the evening when we are reading or writing we prefer it down. Seems much cozier to us. Also there are just the two of us and if we had a couple of kids or another couple it would be a whole other story. We have our routines. I sit on the port side and....
http://purplesagetradingpost.com/sumner ... de-13.html
...run the stove to my left and Ruth sits on the opposite side and uses....
http://purplesagetradingpost.com/sumner ... de-19.html
...our handy little table to fix the meals and then we move it to eat on. She has all of the ....
http://purplesagetradingpost.com/sumner ... de-17.html
....dishes, pots/pans, and silverware handy to her and I have the food handy to me....
http://purplesagetradingpost.com/sumner ... de-13.html
...in the storage compartment.
I usually wash dishes and that is the one thing I do on my knees in front of the sink and the only thing that is somewhat inconvenient.
Enlarging the V-Berth and moving the head looks like a big project, but it didn't take that long and we love both aspects of it. A lot of these projects can be done pretty quickly and you can always go back later and make them nicer.
We are lucky that neither of us is very modest and living together in a small space actually appeals to us.
Good luck,
Sum
Our Trips to....
Our Mac Pages
Mac-Venture Links
Cozy works...that's half the reason for getting on a boat and leaving the crowd!! 
I mean, see what she thinks!!