http://www.ephotozine.com/article/Sigma-55-200-f4-56-DC
http://forums.dpreview.com/forums/re...ssage=23936075
Quote from the site:
"I have owned both the Sigma and Pentax offerings at one time or other, and have been entirely satisfied with both.
In terms of handling, the Sigma has the advantage of being physically shorter at max extension. The Pentax seems all tubes and guts as you extend it, which is a bit alarming to begin with. On the other hand, the Pentax allows you to manually tweak the focus (as with the kit lens).
If I were to choose over again, I'd probably go for the Sigma as it felt more robust and I have a gut feeling (not objectively verified) that it has a slight edge in sharpness.
Mike "
Non of us are really pentax shooters, so it's your call