I also own both the k200 and the K-x and actually it's a great combo together-I've never used the DA50-200 as much as I use it on my K-x and now seriously considering buying the 55-300 too. On the other hand my favourite lens the DA16-45 feels better on the k200 and the same applies to the FA50. I rarely use those lenses on the K-x.
The K-x excellent high iso capabilities and it's responsiveness makes it ideal to use with the longer lenses I if you can live with it's smaller size.
This is how it goes in reality
(two cameras around one neck)
and they fit easily into one small camera-bag with 4 lenses:
Andras