I've had my K-x since July of 2010, and I absolutely love it. It's my first DSLR and I am very happy with its performance, overall. In the interest of improving my photos, but without much in the way of means to purchase, I began to acquire manual focus lenses.
I found manual focus to be difficult with the K-x, particularly with shorter focal lengths. So I was considering selling the K-x and upgrading to the K-r. This would give me AF indicators, as well as interval shooting, which I also wanted. But I had also heard a lot about front focus problems with the K-r. An AF indicator would not help if it did not accurately indicate an in-focus area.
On a whim, I decided to check out the K-7, and it sounded like the perfect solution. Priced used the cost is similar to the K-r. It offers a pentaprism viewfiinder with 100% coverage, as well as AF indicators, so it should be even better than the K-r for manual focusing. And with only one stop less sensitivity than the K-x, it should meet my needs, I thought. After all, I don't use ISO 12800 all that much.
I received my K-7 yesterday and it's a great camera. It is easier to focus (though a focusing screen designed for manual focus would still help). It is, however, noisier than the K-x. Much noisier. And it also loses a lot more dynamic range at high ISO than the K-x. Everything else being equal, I would say that the K-7 is noisier at ISO 3200 than the K-x is at ISO 12800. Here are a few 100% crops.
K-7 ISO3200 1/100
K-7 ISO6400 1/125
K-x ISO6400 1/160
K-7 ISO3200 1/160
K-x ISO3200 1/320
K-x ISO12800 1/160
K-7 ISO3200 1/160
K-x ISO12800 1/160
I realize these are not scientific comparisons; however, I believe that they are informative. It's going to be more difficult than I thought it would be to decide which camera I want to sell. I have to sell one; if I could afford to keep both, then I could afford a K-5!