I now have a new favourite lens - the DA* 300mm was just INCREDIBLE!!!! Probably was used for 1/2 to 2/3rds of the pictures I took in Costa Rica.
My Tamron 70-200mm F2.8 was hardly used at all. There were a few instances were a zoom (like the 70-200 or 60-250mm) would have been helpful as the 300mm pulled in too close, but FAR more instances where the slightly higher magnification was beneficial. Most shots ended up being shot wide open or close to wide open, so again the sharpness of the 300mm was extremely helpful. See pictures below for a few examples.
The WR turned out to be almost a non-event. Only once did I get wet - while I was INDOOR!!!! An exibit with frogs had a constant drizzle, and the K-5 with my 100mm WR was defintely needed, as I and the camera got soaked. The rest of the time, including in the cloud (rain) forest, it was beautiful weather, wit no rain.
I used the Sigma 10-20mm quite a few times, and there was a few instances where the UWA made a difference (see last picture below), but the benefit over my DA* 16-50mm was not as significant as I had expected - probably because I was so busy shooting away with the 300mm
Also someones suggestion that I got a second body was a godsend. Allowed me to have the 300mm K-5 mounted permantly, and then supplement with either the 10-20mm or 16-50mm on the K-x - the latter probably being used the most.
Thanks for all your advice!