Upload & Sell: Off
[Regarding your comparison to the Tokina, it seems to be the exception, rather than the rule. Nearly every other comparison I have seen puts the Tamron ahead. Look again at the Modern Photo test results on Adaptall-2.org. The Tamron easily competes with (and convincingly beats some) OEM lenses at similar focal lengths. The description of performance on Adaptall-2.org is exactly what one should expect from a properly functioning Tamron 17/3.5. Sample variation is significant with this lens, so I am not surprised that one sample of the AT-X beat one sample of the SP.
At this level, copy variation is high. A good copy of any one of these lenses is a value.