From my point of view, size can matter sometimes, but only sometimes, and as Susie pointed out, usually only if the guy is either too small, or too big.
One of my first boyfriends was a professional soccer player from Honduras. He used to receive daily steroid injections in his fanny. Not sure if it's a myth or the truth, as to whether or not steroids cause male genitalia to shrink or grow, but needless to say, he was a very tiny man. He was 28 at the time, and probably had 3 inches erect. Needless to say, ummm, well, I was only 20 then, he was my second, he couldn't please me then, but then I didn't know how to please me then either. But I will be honest and tell you I didn't feel much of anything.
There was the next guy, he was huge, probably 8 inches and thick. Most of the time I couldn't even relax enough to get him past the opening. So he was too big. Again, I was young.
As we age, we learn about ourselves, at least was the case for me. I learned how to relax, how and what pleases me.
Doc is bigger than average, and when we first get together each time there are times when it's still a bit tough to get him in, especially quickly, and the few times when I have gone about things too fast, I have regretted it the next day and was sore or raw.
However, when I am relaxed and I don't rush things, and I need to say that he never rushes, he's usually trying to slow me down actually, it's still a pretty tight fit, and it still hurts sometimes, but it's more of a "hurts so good" type of feeling if you know what I mean?
So, I think that overall size probably doesn't matter all that much unless you have a guy that is an extreme case on one side or the other of the size chart, but for the "normal" man, it's all good.
You have to remember that a lot of women don't or can't orgasm inside anyway, but can, will, and do through clitoral stimulation, so be good with your hands, great with your tongue, and all should be just fine and dandy.
Mashie.