It isnt just about one thing
Being comfortable and enjoying large black men is about a combination of things. For me it is mood, place, timing, and most is in my mind so I enjoy them big if what is happening at the time is exhilerating to me mentally or as you might say if i am very turned on to the man the situation.
Mechanically it is about my vaginal size. I am big down there and used to large men so I can take a fair size but if I am not turned on it can be an uncomfortable experience.
I can enjoy smaller men just as much if they get me into the right frame of mind and are very turned on in return and passionate and also very hard.
I have had 10 inches many times with varied feeling and sensations some fantastic some not so good. Also a lot of very large cocks don't get steel hard and an 8 incher that is really hard can feel like a good 10 inches and be fantastic whilst a soft 10 inches feels like 8 inches.
Yes some can hurt but in the right situation it is part of the pleasure - sweet and sour, pain and pleasure.
I dont think size I think, colour black, mood, situation, the guy and how much fun he is, how creative sexually he is, how accomplished at relaxing me and turning me on. Then size just slips in you might say as I enjoy the pleasureable experience as it happens.