Is the Tamron 24-70mm f/2.8 Di VC USD Lens sharp? This page visually answers that question. Shown above are 100% crops from a lab-captured 70mm f/2.8 test image. Observe the contrast and resolution of these results.
Is the Tamron 24-70mm f/2.8 Di VC USD Lens set to 70mm f/2.8 sharper than the Nikon 24-85mm f/3.5-4.5G AF-S VR Nikkor Lens set to 35mm f/5.6? The image quality comparison above also answers that question. Switch between the results to see the sharpness differences between these lenses.