Originally posted by WalterGA What is it about Pentax's design that prohibits faster frame rates?
The bottleneck is the sensor. The K20D's sensor only got two read-out channels and you just cannot get the data off the sensor any quicker.
The K-7's sensor has four channels and that allows a higher frame rate (including decent video).
Note that the updates to the sensor also had a slight effect on the sensor's noise but I understand that it only very slightly increased, to a negligible extent in practical terms.
It is not easy to compare noise performance even when using RAW files. The K20D apparently applies higher NR even to RAW files (something Canikon have been accused of but only Pentax could be found guilty of doing so). If this is your thing, you can read all about it at DPR (watch for the excellent posts by GordonBGood).
In practical terms, however, only pixel peepers will worry about the noise differences between K20D and K-7. Once some PP has been done, I'm convinced, you wouldn't be able to tell which camera took an image.
I hope that Pentax will make a camera the size of the K20D but with the build quality and the features of the K-7 soon. EDIT: I initially wrote that I found less space on the K-7's grip compared to the K100D's grip. I was wrong. Still, I think slightly larger than the K-7 would suit me.
Everything else about the K-7 is just way better than the K20D, AFAIC. One thing that would really bother me about the K20D -- even if I could have it for a bargain -- is the screwed up AF under Tungsten lighting. The K-7 is the first Pentax DSLR to put that right and that feature alone is a big selling point for me. And then we haven't talked about the other 99 bells and whistles that have been added in comparison to the K20D.