The KP beyond question. With perhaps some patience and careful fishing you should be able to land a good one used with low use, or maybe even a left-over new stock for $1,100 or less. Unfortunately, it was discontinued last year, a step many of us see as a mistake. Coming from the K-x, though a nice little camera and capable for what it is, you would fall in love with the KP!
This would be the one for the long haul. It looks like you have your technique down quite solid, perhaps a good benefit from having to work with the limitations of the K-x, and are not inclined towards the "spray and pray" type of shooting to get results. The higher ISO capability of the KP without significant loss of quality effectively makes your lens having less available aperture more like one that does, while saving weight and cost.
If you like shooting JPEG images right out of the camera, the KP's PRIME IV processor (the same one as in the K-1 II) does an outstanding job. Just be sure to implement "Fine Sharpening" in the Custom Image menus.
It is designed for advanced photographers and professionals needing a more compact body for field use, and to complement the K-1 or K-1 II (which I also have) as the APS-C alternative. APS-C is best for your needs anyway. Sometimes I also shoot indoor sports. So the KP is of first-rate construction, and with a new advanced controls system for greater speed of use and convenience. No "SCENE" modes, however, since it is for advanced users. By now I expect you are beyond such a need. I have owned and used a number of Pentax flagship as well as compact models over the years, and have been using the KP as my primary body for several years. I have liked it so much I bought a second body, both brand new, and have passed over the new K-3 III, buying the K-1 II instead to take full advantage of older but very fine FF glass I bought years ago for my film use.
Last edited by mikesbike; 02-15-2022 at 03:42 PM.