I tested it systematically against both the DA 16-45 (45 mm vs. 50 mm)
and the SMC F 70-210 (remainder of the focal length range). The DA
50-200 is a pretty good lens. It is in the same class as the F 70-210,
which may have been Pentax's best variable-aperture telezoom ever. At
very high magnification one can see that the DA 50-200 is a bit weaker
at the edges than the F 70-210. (Of course, on a DSLR, the edges of the
F 70-210 are not used, while they are on the DA 50-200). Other than that
the lenses are very close, and the difference between them is not
noticeable at lesser magnification.
If I didn't already have the F 70-210 I would get the DA 50-200.
If you do a search on Mail-Archive.com you might find my original post,
which compares the lenses in detail.
Joe