I'm new to Pentax (I primarily shoot mirrorless (EM1, and have a considerable investment in Sony A7rii, A7ii) - however I have rented a number of pro grade DSLR bodies previously for different types of shooting that necessitated one lens or another. Previously I've owned a 5d mk iii.
I was given a loaner of the K3ii over the weekend to test out. Actually having read this thread - I started to get anxious... was I buying into an AF system that is 3 years behind everybody elses. I had no problem tracking and grabbing sharp focus with the 77 at F1.8/F2. Attempting the same with the FE55 1.8 on an A7rii did not yield as positive a result. The Batis 85 didn't do so hot either. This was really a torture test to see how AF system would handle bride and groom walking down the aisle on a backlit day. I asked my model to jog towards me in a zig zag 'Z' fashion (backlit) to see how well the camera coped. The K3ii dropped one or two frames but re-locked focus accurately. I'd reckon out of about 16 frame, 2 were out of focus. My a7rii got about 6-7 in focus. 5d mark iii got a similar amount to the K3ii in focus with the 85 1.8.
Really I found the K3ii no worse than Canon/Nikon D7100/D7200/80d/7d at all and very compliant over a weekend of shooting. I read the thread on optimum tracking settings here at pentax forums - very helpful.
Perhaps not the continuous FPS of the latest 7d mark ii but I did find the K3ii very accurate most importantly. Particularly with newer lenses. Note that I lens calibrated all of the DSLR bodies with lens tune.
The K3ii is quite the machine - I was extremely impressed with AF. As good as any APS-C body I've tried from Canon/Nikon (D7200, 7d, 80d etc...). Where the K3ii sucked was in video tracking.
With respect to Safox 11 to Safox 12. I suspect that the changes go beyond a simple breathing on the Safox 12 module. Both Ricoh reps that I've spoken with in both early March and April made a point that there has been heavy investment in AF technology with Safox 12. Indeed the K1 with 24-70 on demo was incredibly fast and accurate to lock focus in single-af and even C-AF. The Pentax rep that was demo'ing the K1 in Alberta recently mentioned that Ricoh completely overhauled the AF PDAF module, CPU, algorithms for the K1 as they knew it would need to focus in shallower DOF scenarios than their APS-C bodies. One of the advantages of a DSLR PDAF system is that the PDAF points themselves are not constrained to the size of an individual pixel - it is easier to make them larger and more sensitive. In effect todays higher resolution, more densely packed mirrorless sensors need more PDAF points to counter act the smaller more dense pixel pitch. It also makes for good marketing material.