The new TS-E 24/3.5 seems almost perfect:


http://www.the-digital-picture.com/Reviews/ISO-12233-Sample-Crops.aspx?Lens=486&Camera=453&Sample=0&am p;FLI=0&API=0&LensComp=347&CameraComp= 453&SampleComp=0&FLIComp=0&APIComp=0


I'm dying for its full test!