Great read. Although... I have to say, I learned most of this from @mikew already LOL. I have found that this lens is really great, sharp, but does fall off (gets soft) after ~500mm.
He mentions a cpl for this lens. Took a quick look and I laughed. There seem to be two categories - either below $30 or above $300. Guess what kind of quality you will get from that $30 filter LOL.
I always knew what was the weakest part of the Tamron,its called Mike,i will look at them again next year in the hope they are all sorted by then not just some.