Here is my completely idiosyncratic, totally personal, experiential take on this question, which is one I've kicked around with colleagues who are far more PSA-centric than me:
I look for high grade OC cards with eye appeal because that is how I remember them from the pack. Most cards from my childhood (the 1970s) were somewhat OC out of the pack. It doesn't bother me the way it bothers collectors who were kids in later decades when the precision of card manufacturing was just a whole lot better and who've since moved into older cards.
As I shop for cards from my collecting era in a PSA holder what I find is that card classified as an 8 OC or a 9 OC is likely to be pack fresh but for centering. Just the way I remember them. If they are mildly OC and graded 8 or 9 I am just fine with them, especially at the price I can get them. Here is an example of a card that is right in my wheelhouse:
The Carew has the sort of mild centering issue that most of my cards had, and the uneven border of the piping around the team name makes it less visually offensive to me. I paid a lot less for the card than for a comparable card with more wear, so it fits me just fine. If the card is from a set that is prone to centering issues, I am even less inclined to freak out about it. The 1968 hockey issue had really poor centering. This Beliveau card is perfect for me and was a fraction of the cost of a straight 9:
The Dr. J on the right is my favorite ever example. The back of the card is OC but who cares?
A lesser grade is likely to have additional wear to it that has less appeal to me than the OC. If I am looking at a 6-6.5-7 my expectation is that the card will have some corner issues or other wear. In that case I look for the best centered cards I can find, trading off the centering for the wear. An example:
In the final analysis, the question also depends on what your priorities are as a collector. I am not going after cards from my youth to make money, I am collecting them for my own enjoyment. The goal is to have as many of those cards as I can afford that are appealing and evocative to me, not to have a few specimens that someone has determined meet some standard of perfection that I don't really ascribe to. Not to say that I don't occasionally get seduced by a really striking card in a high grade holder; I do:
I just try to shop where the money isn't going so I can indulge my habit at the cost of a bratwurst lunch rather than a steak dinner.