Is the Sigma 150-500mm f/5-6.3 DG OS HSM Lens sharp? This page visually answers that question. Shown above are 100% crops from a lab-captured 500mm f/8.0 test image. Observe the contrast and resolution of these results.
Is the Sigma 150-500mm f/5-6.3 DG OS HSM Lens set to 500mm f/8.0 sharper than the Sigma 150-500mm f/5-6.3 DG OS HSM Lens set to 700mm f/9.0? The image quality comparison above also answers that question. Switch between the results to see the sharpness differences between these lenses.