Is the Sigma 70mm f/2.8 DG Macro Art Lens sharp? This page visually answers that question. Shown above are 100% crops from a lab-captured 98mm f/4.5 test image. Observe the contrast and resolution of these results.
Is the Sigma 70mm f/2.8 DG Macro Art Lens set to 98mm f/4.5 sharper than the Zeiss Milvus 100mm f/2M Lens set to 100mm f/8.0? The image quality comparison above also answers that question. Switch between the results to see the sharpness differences between these lenses.