80-200 image on the left, 28-70 image on the right.
As you can see, the 80-200 F2.8L is very contrasty and sharper than the 28-70 F2.8L at F5.6. This is more pronounced with the uncompressed file in Photoshop. I didn't bother to shoot anything at F8 or higher. A lens is useless to me if it's not sharp by F4.