Is the Sigma 105mm f/1.4 DG HSM Art Lens sharp? This page visually answers that question. Shown above are 100% crops from a lab-captured 105mm f/1.6 test image. Observe the contrast and resolution of these results.
Is the Sigma 105mm f/1.4 DG HSM Art Lens set to 105mm f/1.6 sharper than the Sigma 135mm f/1.8 DG HSM Art Lens set to 135mm f/4.0? The image quality comparison above also answers that question. Switch between the results to see the sharpness differences between these lenses.