Is the Tamron AF 28-75mm f/2.8 XR Di LD Lens sharp? This page visually answers that question. Shown above are 100% crops from a lab-captured 35mm f/2.8 test image. Observe the contrast and resolution of these results.
Is the Tamron AF 28-75mm f/2.8 XR Di LD Lens set to 35mm f/2.8 sharper than the Tamron 28-75mm f/2.8 Di III RXD Lens set to 75mm f/8.0? The image quality comparison above also answers that question. Switch between the results to see the sharpness differences between these lenses.