Originally Posted by rok.my.sox
Hmm not really, once it's in there whatever size it will reach the egg.
Actually yes and no. A longer penis was supposedly important in evolution because it 1) hightens pleasure, making the male seem like a more suitable mate, and 2) increases chance for conception.
But not by much that it wouldn't matter today because we've evolved beyond that now and like Andy said, once it's in there, the deed is done and the chance should be equally considered whether or not your dick's large.