I have no K-3, but I have both the LR4.4 and 5.2 (for Mac). :-)
After downloading some sample files from K-3 I developed them first in LR 4.4 then - in LR 5.2.
File been tested, for example:
Digital Cameras, Pentax K-3 Digital Camera Test Image
Concerning the performance of each LR version:
I did not find any noticeable difference between the LR 4.4 and 5.2 while using any developing tool when the file of 35.3Mb was developed.
Also I did not notice the difference in performance while processing the 24.5Mb from K-5 and 35.3Mb file from K-3 in LR 4.4 as well as in LR 5.2.
It is the easy task for the both versions of software. ;-)
(I have the old iMac from early 2006, Mac OS X 10.7.5)