If a girl told me I was too small, I'd stick my fist in her.
Although I have to fuck giant cock for camera, behind closed doors I lovelovelovelove average-size dick!
It all depends on the girl... all of them are different and get stimulated differently by a cock. Some can't even handle dicks much bigger than average, others can take half a baseball bat. There is no real answer to this question, except to say that if you are much smaller than average, you're shit out of luck... so yes, size matters.