GM take their grading very, very seriously and typically will downgrade a blade compared to competitors. This is why they don't allow retailers to hand pick. I've seen lots of 808s and 606s that were superb, just with minor blemishes. I don't think there's a huge difference between the top 3 grades once they're knocked in properly.
Interestingly, GM don't subscribe to the idea that butterfly marks are a good thing. "Why would you want to have an area of the bat that takes a lot longer to start performing?". My son's had a few bats from GM and all have been absolute guns backed up by a great after sales service.