Current lenses start to show weaknesses already when mounted on 7D (60D/550D) if I interpret DxOMark charts correctly.
DXO does not directly test lens resolution, they test a system resolution, a lens mounted on a camera. Any figures generated only apply to that combination.
I wish that someone had a lens testing setup, but its far too expensive for ordinary mortals, so we only see test results with lens mounted on a camera where the actual lens MTF canot be measured, just estimated. In particular, there can be a lot of error at the edges and corners, where the light strikes the photosites at a angle. Camera manufacturers put more photosites at the edges to compensate for this, and this makes edge measurements which assume the same photosite density as the center questionable.
â€” DxO Analyzer can only be used to test lenses in combination with a digital sensor. A lens by itself can not be tested, and a lens in combination with a film camera can not be tested.
â€” In the case of DSLRs and interchangeable lenses, measurements are only meaningful for a specific type of combination. For example, a 135mm lens on a full-frame Canon 1Ds will measure differently than on a reduced frame Canon 10D. This of course is because much more of the lens is being used by the full-frame camera and therefore most measurements will differ due to the difference in coverage.
â€” Identical lenses, aren't. No two cameras or lenses are the same. Even ones off the same assembly line. It isn't unusual to find significant variance, and indeed some pros typically test a number of lenses of the same brand and type before choosing one.
â€” Only test results of lenses of similar focal lengths should be compared with each other. Long lenses are always going to perform as well as measure better than wide-angle lenses, regardless of brand or price.
â€” Don't compare zooms and prime lenses at the same focal length. With very few exceptions prime lenses will always be superior to zooms. The trade-off is convenience.
â€” Measurements don't tell the whole story. One camera / lens combination may perform better optically than another, yet because of design, handling and other non-measurable performance differences be less desirable for actually producing photographs than one that measures better.
â€” Small differences may not be important. Learn to read the results properly. Just because there is a small measurable difference between one system and another doesn't mean that this difference is necessarily visible on a print â€” regardless of size.