I have a set of these in for my dressage saddle and another set for my all purpose. The weren't super soft at first, but they broke in nicely after being oiled a few times and ridden in. I've had one set for several years now and they still look new.
They haven't streched much, but they do stretch a little, even with the nylon lining. The buckles aren't tiny, but they aren't huge either, and the way the leather is stiched isn't too bulky.
It is only through labor and painful effort, by grim energy and resolute courage, that we move on to better things.
I have the prestige leathers and the nunn finer 3/4 leathers. The nunn finers have held up super well with limited wear and stretch. I got them from Bartville for dead cheap on clearence. The prestige I got on sale and I have them on my event saddles. Even with the nylon you are going to get stretch. I assume less then on my event saddle because you are not putting a ton of pressure on when you gallop and jump with them.
For the buckle issues. The NF leathers actually feel similar in the buckle area. Not too raised.
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I really like my stubbed lined leathers. Since day one they were thin but very strong and buttery soft. I've used them daily for five or six years straight and a couple holes show use but there has been no stretching or discoloration. I have been pleasantly surprised and will definitely buy another pair if these ever die.
Gary Mundy makes nice leathers that buckle from the bottom. If you don't like the conway buckle on his, you can get regular leathers, flip them upside down, and have him make the little sleeves. I did that for some existing leathers.
Bottom buckle leathers are the only way I can ride in a saddle with a wider twist. It makes a huge difference.