I've been with guys as big as 8 to 11 inches (including Greek). I think it depends on how the guy uses it and if I can control the angle and where it hits.
I've had guys that have hit a spot that sends shooting pains into my back and legs. From things I have heard, the lady can expand if she is enjoying it, so size shouldn't be an issue when it comes to length. When it comes to girth, a baby can come out so she can expand in that way too.