3200 is pretty clean and very useable even on the K-70. I have my K-70's auto-ISO set to 100-6400, where the noise is still very manageable. FWIW I've set it higher on occasion and just dealt with noise reduction later. When I had the KP it was set to 100-12800 where noise was still very manageable (A lot of concert/band/backstage existing light).
Since my K1 performed nearly as well as my KP in low light it seems extremely likely the K3III will well-exceed the low-light capabilities of the KP and of course your K3. IMHO it may well be the end all in an APS-C regarding ultimate image quality, and in particular ISO performance.
It should be a great concert camera
Low-light, burst speeds, AF, decent video performance when needed.... Got it all from what I'm seeing.