I currently have a Pentax FA 80-320, and it's very nice to have a long zoom available. Lately, I've been considering "updating" to the DA 55-300.
I also have the DA 50-200, so the lower end of the range is covered, although I suppose I could replace both of those with the 55-300. I don't think either of my current lenses is in high demand, so I probably wouldn't get much for them.
Are there any significant differences in optics? What about the auto focusing? Any other factors that I should consider in my decision?