I think your comparison is about lenses and not IQ of the bodies. They use the same sensors, have virtually the same noise levels and I have not seen any sharpness difference worth noting. The 17-55mm is a cult lens for 1.6 bodies (IS, fast aperture, good sharpness) so I am not suprised that you find the IQ on your 60D is much better. But not because of the body.

Cheers,
John.