Here is the latest shootout lab measurebation by Falk Lumo (aka Falconeye), which I think is scientific, of good quality and higher level standard. Go read, inspect and measurbate yourself and the results (and conclusion(s) drawn up as well) may surprise you!
http://falklumo.blogspot.com/2009/10/lumolabs-pentax-k-x-vs-k-7-sensor-and.html
Yet, there is another comparison made between the K-x and K-7, by the "Pentax is Death" guy (aka Ogl). Full size sample photos are posted.
http://fotkidepo.ru/?id=album:24445
I think both guys have done an objective enough tests and the results obtained are of certain good reference values. I won't write further here about my observations and comments and would just let you go figure out yourself and make your own judgement!