Is the Tamron 17-35mm f/2.8-4 Di OSD Lens sharp? This page visually answers that question. Shown above are 100% crops from a lab-captured 20mm f/8.0 test image. Observe the contrast and resolution of these results.
Is the Tamron 17-35mm f/2.8-4 Di OSD Lens set to 20mm f/8.0 sharper than the Tokina 17-35mm f/4 AT-X Pro FX Lens set to 28mm f/5.6? The image quality comparison above also answers that question. Switch between the results to see the sharpness differences between these lenses.