Out of all the times I've submitted modern books to CGC, not once have I ever recieved anything higher than a 9.8.
The very first comic I ever submitted was a Walking Dead 1. I bought it when they first hit the shelves, and I immediately bagged/boarded it, and I don't think I ever read it. It was honestly the nicest looking book I'd ever seen, basically flawless. It came back as a 9.8, but I was still happy about that.
Btw, this is the only 9.9 in my collection, and the only 9.9 I've ever seen in person. It doesn't look any better than the Walking Dead 1 I had. Would love to see a 10 in person for comparison sake.