I went from a K10D to a K-3 this last Spring. The migration was fairly painless and the K-3 is an incredible tool. That being said, any of the currently available Pentax models (with the possible exception of the K-500) will be step up in both image quality and features from your K10D. By step up, I mean superior AF, exposure accuracy, and speed of operation.
Here are some bullet points:
- For value and features the K-5 IIs is pretty hard to beat while it is still available
- The K-30/50 lacks the top LCD and metal build, but is a ton of camera for the money...light weight too
- The K-3 is a lot more money than current pricing for the K-5IIs, but is also a lot more camera
- You can tell the difference between the 24 Mpixel and 16Mpixel output, but it is not huge
- It is worth the time and effort to figure out the differences in the features between the three bodies
As I noted, I chose the K-3, though I was highly tempted by the K-50. A close friend has a K-50 and it is a very nice camera. I might also have bought a K-5 IIs except that the price at the time for body only was almost as much as I paid for the K-3 with lens and grip. At current pricing I may well have bought one.
That being said, I have no regrets with the K-3 purchase.
Steve