doesn't it also depend on how that dick is used, how experienced the guy is at taking dick, how much prep is done by the top guy to loosen up the bottom guy, even how much trusts do you share?
even a small dick will hurt if its just jabbed in with no preparation - so both a very long dick or very thick dick can cause equal, if different pain?
But all things being equal I'd think a thicker dick would cause more discomfort than a long one?