I’ve seen a recurring question pop up on the dpreview forums: how much sharper is the IS version of the 70-200mm f/4 lens vs the non-IS version? The answer: On the 5D Mark II the difference isn’t noticeable in the center. On the 18MP crop bodies (7D/T2i/T3i/60D), the difference is noticeable, as is typically the case when evaluating different classes of lenses on higher pixel density cameras.
Here are the two lenses on the 5D Mark II, shot from about 15 feet @ 200mm f/4. Click on the image for a full-sized 100% center crop.
Here are the two lenses on the T2i, shot from the same distance. Click on the image for a full-sized 100% center crop.
All samples were manually focused in Live View, shot raw and processed with default settings in LR3. When you click through the images you may need to click a second time to get your browser to show you the full 100% view.