Ouch, this one hurts. The front cover looks like a 9.2-9.4. The back cover water stain, though faint, is across almost the entire top edge. We know that CGC is very harsh on water stains and any stains/soiling of any type, though it's uncommon to find a CGC graded book that is otherwise NM with a large water stain as the only defect. Someone previously posted a Conan #1 that looked NM at first glance, but had faint water stains / tide lines throughout the entire book from front cover to back cover and everything in between. It was pressed flat without wrinkles and otherwise no defects and graded a CGC 4.5. My guess is:
CGC 6.5 - 7.0