The K100D lacks sdm and is only 6mp but has a CCD sensor which some find renders colors different than the CMOS sensors in the other two cameras. I have not ever shot a K-x. I owned a K-50, I currently have two K-3's and a K100D and a K100D super. I keep the K100D around for converting lenses from SDM to screwdrive and the K100D Super is a bit of nostalgia for me as it was my return to SLR photography camera after a long hiatus. The K100D (and super) use a Pentamirror which is darker than a pentaprism which may be a consideration - I'm not familiar enough with the K-x to say. Finally the the sales prices of the K100D mean that I am not inclined to sell mine - there isn't a lot to be gained from it and my sentimentality keeps it on the shelf. The K-x market is unknown to me.
I'm sorry if that doesn't help. It's all I can offer.
Edit: I erroneously said the k100d lacked image stabilization originally.
Last edited by UncleVanya; 09-22-2016 at 12:02 AM.