Is the Nikon 80-400mm f/4.5-5.6D AF VR Nikkor Lens sharp? This page visually answers that question. Shown above are 100% crops from a lab-captured 135mm f/8.0 test image. Observe the contrast and resolution of these results.
Is the Nikon 80-400mm f/4.5-5.6D AF VR Nikkor Lens set to 135mm f/8.0 sharper than the Sigma 120-300mm f/2.8 EX DG HSM Lens set to 300mm f/4.0? The image quality comparison above also answers that question. Switch between the results to see the sharpness differences between these lenses.