I use a K100D Super, mainly chosen to be able to use my deceased (long before I came around) father-in-laws old Pentax lenses. A camera is only as good as the glass it takes a picture through! With the exception of my Sigma 70mm 2.8 macro, the old manual lenses I have are all much better and sharper than my newer lenses. I have the kit 18-55 lens, which is nothing to write home about. Have the Tamron 70-300 1:4 LD Di, which I regret buying because of its chromic aberration problems at anything over 150mm or so, and its need to be stopped down to f8 for any kind of sharpness past 150mm. I get much better results for distant pictures with my Canon S3IS, or the 135mm manual lens.
The old lenses, including a M 50mm 1.4, 28mm 2.8, and 135mm 2.8, are just wonderful. Sure you have to manually focus...but let's face it, Pentax isn't famous for it's autofocus anyways. You really get what you pay for. I've come to the conclusion that for a newer lens, it costs around $400 to get something of good quality. If I were you, I would sell the 50-200 and the 70-300 and try the Pentax 55-300. It will cost a little bit more than the 50-200 and 70-300, but from reading reviews and seeing sample pictures, it does a better job than either. And, its is one lens that will do the job of 2 you currently have. The Sigma macro I have is awesome, sharp from edge to edge even at f2.8. Next on my list is a wide angle, something like the Sigma 10-20mm. After that, sell off the Tamron 70-300 and wait for the Pentax 60-250(?) to come out and see if it is any good.
