Originally Posted by ricardobeat 
If the 55-300mm comes out as "comparable" to the Tamron, THAT would be a real shot in the foot. That lens is awfully soft after 200mm, and not great at any length. The 18-250 is much better but not stellar either. I think they're aiming for high quality glass, not just another consumer zoom.
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