I purchased the 24-70 2.8L and was expecting a superb lens for the price.  After comparing with my 70-200 4L, the 24-70 performed worse at 70mm f4 than my 70-200 4L.  At 35mm, the sharpness was only average, slightly less than my 28-135 at f4.  The image does get sharper as I increase to f8 or higher, but the whole purpose of getting this lens is for the f2.8. The color and contrast was outstanding as expected from Canon L series.  The lens is also big and heavy, not a lens you want carry around your neck all day.  It's not very practical lens for me and copy I got doesn't perform up to optical quality I expect.  I won't bother send it back to Canon for calibration.  It's going back to the store.
I purchased the 24-70 2. 8L and was expecting a superb lens for the price. After comparing with my 70-200 4L, the 24-70 performed worse at 70mm f4 than my 70-200 4L. At 35mm, the sharpness was only average, slightly less than my 28-135 at f4. The image does get sharper as I increase to f8 or higher, but the whole purpose of getting this lens is for the f2. 8. The color and contrast was outstanding as expected from Canon L series. The lens is also big and heavy, not a lens you want carry around your neck all day. It's not very practical lens for me and copy I got doesn't perform up to optical quality I expect. I won't bother send it back to Canon for calibration. It's going back to the store.