Originally posted by Tex I have a Tammy 70-200 f/2.8. It does a very good job at 800 or when I shoot daylight games.
Specifically it is the noise at the higher ISO settings that is the problem.
I bought the Tamron lens because it was the first that I could get for the Pentax mount.
I also have a slow Pentax 300 zoom that shoots very good images... but needs light!
In re-reading the rest of your post, you have NR set to high, this will take away sharpness.
By the way, what do you have sharpness set to, as it can add noise also, and if we are discussing these settings does that mean you are shooting JPEG?
Also, I might suggest that you go back and re-start your settings process. Put everything to neutral, take some benchmark shots, and then move adjustments either way from neutral, one at a time and see the impact. Tune the camera for the ISO you intend to use and refine these settings. I would be surprised if you can't get things better right out of the camera. I have the K7, not K20 and I find no issue at all stepping up to ISO 800 for many shots, using a much slower 300mmF4 and 1.7x AF TC
I have not yet played extensively at higher ISO settings, but never had an issue with my *istD or K10D pushing all the way to maximum of 3200 and 1600 respectively.