This is a funny discussion. The Human eye is the worst resolver at about 2-3MP. Then there's CA, distortion and all that stuff going on in our eyes that's corrected by our brain.
Then there's viewing distance: A 5x7 looks fine at 1 foot distance but at 2 feet distance, a 8x10 is its equivalent. A 40x60 at about 10-15 feet is the equivalent of a 5x7.
My 20x24 prints look brilliant on a wall. My 8x10s look like schmuck on a wall. It's ALL in the viewing distance. Remember, the human eye is not a telescope and its resolving power is terrible. It's all about equivalencies. And what kind of moron would judge a 40x60 at a foot distance?