Originally Posted by raz 
you are talking about the 70-300 ? If yes, then is not in any way "awfully soft after 200mm", maybe you are talking about the sigma, but the tamron 70-300 has decent quality all over the range. It is not stellar but no soft either.
Here is a shot at 300mm f/5.6 no sharpening, no nothing
http://raz.ro/pentax/70-300/imgp6047.jpg
Please mind reading the quote. I was talking about the 28-300mm. The 70-300mm is sharper, but not great either and the purple fringing scared me away from buying it in less than 5 minutes (ugly 2px fringe on indoor tungsten lighting, come on!).