Originally Posted by codiac2600 
The onloy thing you're no considering is the 55-300 is an extremely sharp lens and overlap wise provides the least amount of overlap with the new kit lens. The 55-300 is designed to be sharper edge to edge for the K20D and I don't think any of the Tamron super zooms will compete with contrast and sharpness with this lens. It's just my opinion but I loved it and the build quality is great.
did you get a chance to take some sample shots with the 55-300?
i'm also seriously considering this to supplement my sigma 17-70.
price is ok at 350, MFD could have been better imho.
but if quality is good, i'll take it.