I went from K-50 to K-3 when the K-3II was an option also. The K-3 (like the KP) offers an onboard flash. The K-3II has an onboard GPS rather than flash. I suspected (and still think) the onboard flash is more useful to me. I do miss the Pixel Shift features for landscapes. As for the KP - I have never used it. I do however like the battery life of the larger battery more than I liked the battery life in my K-50 - but this is a MINOR issue.
The larger benefits were moving from 12 bit to 14 bit raw, moving from 16mp to 24mp, improved autofocus, improved metering, etc. The larger buffer and higher frame rate were also beneficial in niche situations.
The KP unlike the K3ii offers the accelerator chip for improved high ISO output. The KP like the K3ii offers a battery grip - the grip uses the larger battery which means managing two types of batteries for the KP if you want to use the grip.
Finally from what I have read the KP grip - despite being available in 3 sizes - is not loved like the K-3/K-3ii/K-70/K-50. If you love the grip on the K-50, the K-3ii is likely just up your alley.
---------- Post added 10-22-18 at 02:28 PM ----------
Originally posted by Agi I forgot to say, I'm a portrait photographer, I shoot specially outside in the street.
The smaller KP may make the most sense then. I'm a fan of the K-3 ergonomics but the size isn't the best for street (although it isn't terrible at it either). For Street Portrait work the DA 40 is my favorite - very short and not intimidating. The DA 70 is another option that is diminutive also.