Is the Sigma 70-200mm f/2.8 EX DG OS HSM Lens sharp? This page visually answers that question. Shown above are 100% crops from a lab-captured 280mm f/5.6 test image. Observe the contrast and resolution of these results.
Is the Sigma 70-200mm f/2.8 EX DG OS HSM Lens set to 280mm f/5.6 sharper than the Sigma 70-200mm f/2.8 EX DG HSM II Macro Lens set to 100mm f/3.2? The image quality comparison above also answers that question. Switch between the results to see the sharpness differences between these lenses.