I'm in the same position as you, halfspin, and for me there is NO doubt: Long glass on the K-3, landscape lens on the K-5.
The K-5 is a great camera, great dynamic range and with a good landscape lens I believe it has all the resolution you could dream of for landscape photos. For birding you will need 1) fast AF and 2) room for cropping - and the K-3 is promising to be an improvement for both these needs. I am also hoping for slightly less noise at four-digit iso - which would be relevant for 1/1600 sek bird-in-flight shots.
In December I see myself in some beautiful winter landscape surrounded by flocks of migrating water birds, with the K-3 plus my DA* 300mm at TAV:1/1600sek;f5.6, and the K-5 with my DA* 50-135mm at AV:f8 (right, I prefer short tele even for the scenery - I'm a beauty-in-the-detail observer, I suppose). I'll have the Sigma 28mm as a K-5 backup for landscapes - I won't miss any bird shots switching, then.
...I don't know why I am out there in December rather than at work, though? Hmmm... Maybe I got fired for browsing pentaxforums and dreaming of the K-3 during work hours?