Is the Tamron SP AF 90mm f/2.8 Di Macro Lens sharp? This page visually answers that question. Shown above are 100% crops from a lab-captured 90mm f/2.8 test image. Observe the contrast and resolution of these results.
Is the Tamron SP AF 90mm f/2.8 Di Macro Lens set to 90mm f/2.8 sharper than the Tamron AF 28-75mm f/2.8 XR Di LD Lens set to 50mm f/5.6? The image quality comparison above also answers that question. Switch between the results to see the sharpness differences between these lenses.