Sigma 55-200 vs Pentax 50-200?

[Glen]

I've been looking for zoom lenses made specifically for the new Pentax 
digital cameras, and found these two similar lenses:

Pentax smc P-DA 50-200mm F4-5.6 ED
Sigma 55-200mm F4-5.6 DC

The Sigma lens is definitely the more affordable of the two. Is the image 
quality actually noticeably less than the Pentax lens? Does anyone know the 
advantages or disadvantages of each lens? Is there another brand to 
consider, which covers this same range of focal lengths?


thanks,
Glen