I've had two partners in the double-digits, as you put it. I don't remember how it felt when I was getting used to the first (and smaller) of the two. Was another me. Fourteen years ago. But, near daily sex with that guy for six years made it a custom fit after a while, and the sex was great. We're both married now, and the tension is through the roof when we see each other. He picked up herpes somewhere, so that's never going to happen again. Very recently, I started hooking up when I can with a guy who has an inch more than the other guy, in each direction. Other than that, they are the same body type.
The second one is definitely at my limit. I can't fit him in if I've ovulated. I want him to fully penetrate, because I want to feel our pelvises (pelvi?) touching at the end of each stroke. It does feel entirely different with him when he gets all the way in. There is a palpable difference for me between feeling filled up, and feeling filled up to maximum capacity. There is some fear, and sometimes a bit of pain. The physical sensation is not one I have words for. I don't know how to describe the difference the inch in length and the inch in girth make. I just know it is there. Still, I don't prefer one kind of good feeling over the other. My husband's got about half the length, and nearly two inches less girth, and I still love the way he feels inside me.