Hi fccwpe,
If it were me, I'd give the Kx. I currently use a K20 and a K-7 side by side, and the commonality between the user interface makes switching from one to the other a lot easier. I access controls a lot, and having the two wheels has just become part of the way I work in the field.
I also have a DS and a K100DS, and Ive found that switching between one of these and the K-7 is sometimes confusing to my little brain. . .
To me, the way the camera handles is more important than the IQ differences between these two bodies. With the K-5, you should still get the high ISO performance, and the K20 would give you the handling advantage in situations that you don't need the sensor sensitivity.
Of course, YMMV. . .
Scott