I have a tilted cervix which limits me to around 8'ish inches in length. Girth is not a problem, the bigger the better. I love a very hard, fast and furious pounding doggy style, but anything too long will spear my cervix, which is exceptionally painful. I can manage slow movements, but it takes a bit of body maneuvering to find the right comfortable angle. I can take much larger at other angles, such as on my side.
There are a couple of males the local house parties who I limit my play with for this reason. I've told them why and they understand. Periodically I get an idiot male who tells me I just need a good stretching out and he can do that for me.