Is the Nikon 600mm f/4G AF-S VR Nikkor Lens sharp? This page visually answers that question. Shown above are 100% crops from a lab-captured 1020mm f/7.1 test image. Observe the contrast and resolution of these results.
Is the Nikon 600mm f/4G AF-S VR Nikkor Lens set to 1020mm f/7.1 sharper than the Nikon 500mm f/4G AF-S VR Nikkor Lens set to 500mm f/4.5? The image quality comparison above also answers that question. Switch between the results to see the sharpness differences between these lenses.