I use the k-5 and the da*300 and the combination is just fantastic! I also have the 1,7 afa, and although people seem to like that combo I honestly don't like it much. With tc the image quality is very notably degraded, and also your viewfinder goes darker. In my limited experience with the TC, I find that just cropping images from the da*300 produces better and easier results. Maybe my technique is poor with the tc, I don't know.. A few looks great, but I find it to be highly inconsistent. As to the macro capabilities of the lens; well it's a telephoto lens not a macro
But also here I find that just cropping (the lens is very sharp) makes for good close ups.
I added an example. Please bare in mind that this is just the first example I found on my drive, and it is a snapshot also. It should give you a pointer to how crops looks though.
First image is full frame shot (un-cropped) :
Second is a 1:1 crop of the bee:
Looking at it now I'm not even sure the bee is entirely in focus hehe, but I think you get my point that this lens can be cropped heavily with pretty good results.