http://www.the-digital-picture.com/Reviews/ISO-12233-Sample-Crops.aspx?Lens=278&Camera=963&Sample=0&FLI=0&API=0&LensComp=972&CameraComp=963&SampleComp=0&FLIComp=4&APIComp=0
On a side note, Brian "Finally" put a new sensor behind the 400f5.6 (I'm using the 7D2 for comparison since this is the best "budget" supertelephoto on the market).
23 years ago, Canon did something really, really right.