I think the K5 IIs is just too old to consider buying (which is a different argument than already having one and deciding if you should upgrade it). The K3 II is getting up there, but has features the KP doesn't including a higher rated shutter lifespan. The KP may have better image quality, but obviously more expensive.
So the first question to me is what are the price differences, and is the KP going to deliver on that higher quality in a meaningful way to you. It's easy to compare specs on paper, but what really matters is real world results. I've seen fantastic images from most anything. One of my favorite shots I took was on an 8MP Olympus E-500. Aside from the resolution, I doubt there's anything even the KP could offer to make a noticeable improvement on that specific photo. Since I only view it on a display, even the resolution isn't a problem.
Another way to put it is let's say it's a $300 difference between the K3 II and KP. Are you going to see a $300 improvement in the photos? And even if the answer is yes, how is it better? Dynamic range is a big one, and my K3 II has performed well with anything I've thrown at it so far. Take a look at my gallery (it's not very big), and pay special attention to my steel wool and night time jet car photos. For the price differences I saw, I'm more than happy with this over the KP.
Scott Monroe | Flickr
Noise is a big concern too, but a dedicated noise reduction program can work wonders. I shot a lot at ISO 1600 and 3200 at the races. At 1600, things were acceptable. At 3200, it became a noisy mess. I ran some of them through Topaz DeNoiseAI and it was like, "what noise?" There overall image quality didn't suffer too much either. So why spend extra on the KP when I get great results in post for much less?
The caveat here, though, is your skill and desires. I'm just a hobbyist, so I don't mind making sacrifices to save a few bucks. If I were getting paid for my work, then that changes things. Suddenly having that better IQ right from the camera and quicker turnaround times may be needed to keep clients happy. Then again, that second card slot on the K3 II could be the difference between taking a bit longer to deliver the photos vs not delivering any at all due to memory card corruption.
The second big thing I considered was ergonomics. Subjective, but the KP just looked uncomfortable to hold. The K3 II fits like a glove and I love not having to reach back to press the shutter.
So for me, it is the K3 II hands down, or the original K3 if you need a built in flash and don't mind losing Astrotracer out of the box.