The results from the first Tamron 28-300 VC we tested were ... not good. The second lens is "clearly" superior to the first and the results from this lens are now shown as the default sample "1". Here is a comparison between the two Tamron 28-300mm VC PZD lenses.
Here is an interesting image quality comparison: Tamron 28-300mm VC PZD Lens compared to the Canon 28-300mm L IS Lens.
Specifications, measurements and standard product images along with a variety of on-camera imagery are also now available for this lens. Here is an interesting size comparison: Tamron 28-300mm VC PZD Lens vs. Canon 28-300mm L IS Lens.