You will see a truly substantial difference at ISO 6400, both in lower noise and in preservation of detail. Check the figures on the Fiddlers Ale and Hellas wine vinegar bottle, check between the bottles in shadow areas, check the shadows just beyond the last Samuel Adams beer bottle and the writing on that bottle, and also the squares in the color chart. The KP's performance in low light really got my attention together with its smallish design.
I have had my K-5 IIs for quite a while, and love it. I got a steal deal buying it as a new-left over after the K-3 appeared. I will still keep and use it even after I get the KP. It even slightly outperforms the K-3 in higher ISO use, in fact it is quite exceptional in detail preservation. But the KP leaves it behind for noise control with preservation of detail at higher ISO use. The K-5/ K-3 series are different in control layout than the KP. Both they and the KP are designed for advanced serious users, the KP being a new, more compact concept in this area. When to use either depends on what your uses and needs are. I think the K-5/K-3 controls are unsurpassed under circumstances where very quick changes may be needed in ISO, metering mode, etc. With the KP, the new controls serving its compactness are programmable and reportedly quick to use, but not as separate and dedicated as those of the K-3/K-5 are.
When a lot of portability is the issue, and/or if shooting in low light, a smallish kit with the KP would be tops. A very high caliber compact outfit. The KP seems ideal for this kind of activity. I often do this kind of thing, on foot or bicycle. When out and about for hours with camera in belt holster plus cross-shoulders strap, any difference in compactness and weight is noticeable. I have long had several Limited primes and recently bought another- the 15mm f/4 as well as the 20-40mm WR Ltd. At the same time, the design of the KP is such that it is expandable to being a more fleshed-out body for use with a larger kit for say shooting low-light indoor events with larger lenses.
Last edited by mikesbike; 04-17-2017 at 12:34 PM.