Regardless of the "official specs" this is what I have experienced.
-The K-7 has a much better feel in my hand and feels bigger however the K-x is my go-to camera for its light weight and compact size.
-The K-7 performs much worse at high ISO. The K-x beats the K-7 hands down at +800ISO. I only bring the K-x if I am shooting at night.
-The K-7 autofocus performs much better than the K-x. I have consistently gotten more focused shots with the K-7
-The K-7 has a steeper learning curve. More custom settings than the K-x, this can be a good or a bad thing.
-The K-7 is weatherproof, the K-x is not.
I could go on and on.
In my experience I actually only bring my K-7 on "serious" shoots, I want better quality and more options. The K-7 fits a certain niche, although at night forget it. The K-x though, is my go-to bring everywhere camera.
The K-x is always on my side for every day usability. The K-7 is my pro shot camera. Although I would say that I have captured a higher number of great shots with my k-x than I have with my k-7. But maybe that is only because I have used the K-x more. I don't know.