To me sharpness is not really important when it comes to comparing one L lens to another, I think both the 24-70 and the 24-105 are really sharp for most of the stuff people do, one may be slightly sharper than the other, so what? To me what important is detail, you and I can easily increase the sharpness in photoshop, but you and I cannot add more detail to the image...The detail may be a little soft, but it's available, you can't enhance something that isn't there. L lenses have the amazing capability to capture details.