^ The K-S2 is a nice camera, but it's not on my upgrade list. I want 14 bit RAW files from my next camera.
The 14 bit RAW files make a pretty big difference at higher ISOs. Comparing the K-30/K-50 12 bit files to the K-5 & K-5II 14 bit files, the difference in image quality can be noticed from ISO 800 & above. At ISO 6400, the K-30/K-50 lag pretty far behind the K-5 & K-5II. The color & fine detail is far more accurate with the K-5 cameras. The K-5IIs is about the same, but sharper since no AA filter is used. There is some false coloring & loss of fine details in the K-30/K-50 12 bit raw files, but they still look very good.
I'm still quite impressed with my K-50's high ISO abilities, though. I couldn't really shoot past ISO 400 with my old 10MP Sony A200 DSLR camera. Sometimes I would shoot up to ISO 800, but I would usually get very grainy & harsh looking pictures. ISO 1600 was pretty much unusable & there was no sense in even using ISO 3200. I can shoot up to ISO 12800 on my K-50 in a pinch.