My 7D gives me around an extra stop in comparison to the 40D in terms of noise, but it obviously isn't as clean as the 5D MkII. In fact, I find it superior in every way ot the 40D, but it is less forgiving. The higher resolution magnifies all the imperfections of lenses and slight motion blur or focus problems, each of which will soften the image, but reduce the image to that of the 40D and it will be just as sharp, plus you have more latitude in ability to sharpen images in post. While the 5D MkII does produce higher image quality, with fast moving action, it will start to show its inadequacies, particularly with tracking focus, although for static scenes, in low light, it will have better focusing than the 7D if the centre point is used. Also, you will have to be much more careful about timing the instant, to get the shot you want, due to the slower frame rate.