The K7 image quality at ISO 6400 is quite usable, and responds well to third party noise reduction. Here is an example.
First the unaltered image, taken at 6400 on the K7:
Here's a 100% crop before any noise reduction is applied:
Then after the application of chroma noise reduction in Lightroom 3 (Beta 2):
Then adding Luminance noise reduction to the image as well:
There is plenty of tweaking you can do to optimize image quality, but the above examples show what you can do with just gross adjustments of the NR parameters. I would probably never apply that much NR in any image, but you can see that you have lots of control with sophisticated NR routines with not a lot of image degradation.
Do not be afraid of the K7's high ISO!