Just noticed this group. My K-3 arrives tomorrow and I am looking forward to using the Live View focus peaking for Macro photography. I have a number of old school macros - including three 1:1 macros, I have bought over the past year but have not used. I have a feeling that working with these lenses and focus peaking is going to be fun.
I also have the SMC 500 plus the 1.4L rear converter and again, focus peaking is going to be a real boon with this lens and TC. I tried putting a split screen in my K-5 but was never really happy with the results - close but no cigar.

I may be off base but having focus peaking available will breathe new life into many old lenses.

I shoot my Pentax lenses manually on a Sony NEX-5N, and I have to tell you focus peaking is just awesome. No squinting or worrying, no thinking, "Is it sharp or does it just look sharp on the screen?" Just wait for the focus peaking color and go.

My 5N, with the focus peaking, the high-ISO, and the lens-booster, is as close as I think is possible to come to actually "cheating."

I took the K-3 with the SMC 500 4.5 lens plus 1.4 L rear adapter out in the back yard. I wear glasses and focusing this lens was always difficult for me, focusing this lens with the 1.5L rear adapter was more difficult. I am pleasd with live focus on the K-3 and look forward to using the numerous manual focus lenses I have, especially the macro lenses, and achieving better results than I have in the past.
I am unable to post photos here but I do have them posted elsewhere see if this link works https://www.pentaxforums.com/forums/122-lens-clubs/55946-300mm-plus-lens-club...ml#post2582251

The first image is no cropping, right out of the camera. the second is a 100% crop image.