I really should make a shot of the pear with a bite out of it, to signify the end of the test.
I opened the first image in Photoshop CS3, increased the exposure a little; sharpened to the 100 indicator with the sharpen slider in the Sharpen tool and then applied the same parameters to each of the other shots.
I shot one shot with the 18-55mm lens at fixed ISO200 and then a shot at ISOauto. I did the same with the 12-24mm lens.
The ISOauto setting accounts for why one shot is at ISO720 and one shot at ISO640. I don’t think the difference is significant.
All shots were taken with the focal length set to 24mm.
After I had opened the four shots, I set the rectangle tool to a fixed size of 475×475 pixels in each case. I then copied that section of the photograph into a ‘new’ image and saved-for-web.
Judge the sharpness of each for yourself.