Originally posted by UncleVanya diffraction only cared about the pixel size
Pixel size for "usual" approaches is completely irrelevant, unless your approach is to look at the pixel level (which is completely valid, but a very different one).
If that is the case though, you'd need to only consider this with regards to diffraction, but with regards to all effects.
For a starter for dummies you'd also have to only look at the "screen" tab on DxOmark for any results for example.
Which then will quickly lead you to understand that you gain absolutely nothing from a FF sensor.