My 2c...
While the K-3 may have a higher resolution sensor at 24 MP than a K-5/ii/s/50 at 16 MP, its easy to get caught up in the "megapixel wars" that are often created by camera companies or enthusiasts. Yes, there will be more resolution in a K-3 image, but the bigger question is do you really need that extra resolution. Going from the K-x 12 MP sensor to a 16 MP sensor will not only give you 4 extra MP, but it will give you a lot of extra things that are often overlooked. Not only is the higher ISO better (in terms of noise quantity), but the noise that exists is easily reduced in post processing. The dynamic range on the 16 MP sensors was the best on the market when they were released, and still are way up there. These bonuses are also evident in the 24 MP sensor on the K-3, but arent any more of an improvement over the 16 MP sensors...which means the only real improvement from the 16 to the 24 MP sensors, was the bump in resolution...
Personally owning a K-5, (and a K10) Ive yet to find a situation where I wished I had MORE resolution. I regularly print my images from 8x8 to 16x20, and the 16x20s I have done look amazing (from the aspects of noise and resolution...not necessarily on my photographic ability
). Many of these images could print even larger before the need for more resolution became a must. While Im not going to say 24 MP is too much or overkill, I find that the 16 MP in the K-5 body seem to be plenty for the vast majority of printing work that most people would do. Additionally, something to consider is the change in file sizes with a larger resolution sensor. My 10 MP K10 produced 16Mb RAW images. The K-5 produces 24-26Mb RAW images. I believe the K-3 produces 35-40Mb RAW images. For what its worth youll definitely need larger and faster cards with a K-3 and a fast enough computer to handle post processing files of that size (should you choose to).
None of this is meant to steer you away from the K-3, cause I certainly wouldnt say 'no' if one was given to me. However, if someone asked me to trade my K-5 and my DA* 50-135 for a K-3 and 55-300 WR, Id tell them very politely to go to hell. Id MUCH rather have a body that is a generation old with high end glass vs the latest and greatest body with consumer grade glass. Higher MP count wont necessarily make up for the loss in high quality glass. In the Pentax world lenses are forever. Bodies are good for 5-7 years. If I were in your shoes, Id look at better glass with a K-5/II/s/50 body vs a K-3.