The Munson could even get a half-point bump for better than average centering for the grade, or it could get a 7 straight.
And although PSA has semi-well worded descriptions of grades, there are times when the grades you get back don't make sense. At first I thought one of the stains on the front of the McCovey was a pinhole as well, which would have dropped it to an automatic 1.
If you decide to apply for oldbaseballcards, their grading scale goes like this:
http://www.oldbaseball.com/funstuff/Gurugrading.htm