I had a chance to make some rather hasty tests of these two Pentax lenses.  Taken at f/5, and shot to match exposures, the conclusions are expected: the 16-45 shows better resolution near the edges but both are similar near the center.  This Picasa collage isn't intended for deep inspection, just shows that both took a nice image overall.  So other than weather-resistance and range the general results are pretty similar.  
