This is probably an over generalization, but my theory is if these same cards were graded 6 and 6.5, the 6 might sell for more because in my opinion there is a slight diamond cut to the 8.5. I'm not saying that there aren't any discriminating high end collectors, but I think there are more who buy the card over the flip at the mid to low end of the grading scale. I've seen 5s sell for more than a 6, etc. To be fair, I don't really watch auctions when the grade is way out of my price range though, so I'm not watching a lot of auctions for cards graded 8+
