Hmmm. The laws of physics would suggest you'd only see a side by side difference only when zoomed in over 50 - 60% where the detail is expanded. There simply aren't enough pixels on the screen to show anywhere near the detail resolved, even a 6MP camera on a 720p screen! So on a higher MP camera the screen just throws away the extra pixels at screen size, the more MP the more pixels the screen dumps. Actually, on a 720p set up, make that about an 80% zoom for circa 20MP bodies and above. It won't be MP making that difference, it's more likely you'll see a very significant difference with the ability of different lenses to resolve detail, alongside better DR combined with better SNR ratios on newer sensors (and larger sensors).