It depends on your appetite for post-processing, the software tools you're using, your skill in using them and your expectations of the final result - including the physical size and intended medium for reproduction.
I can't speak knowledgeably for the K-70, but I frequently shoot my K-3 and K-3II at ISO 6400 without any qualms whatsoever. I shoot RAW, and expect to do some colour noise reduction at higher ISOs. Depending on cropping and the final reproduction size, I add some mild luminance noise reduction too. After processing, such images typically display well on my 17" laptop and 23" desktop monitors, and - from a sensible viewing distance - my 40" LCD TV.
I have plenty of shots taken at sensitivities above ISO 6400 that are more than serviceable... right up to ISO 20,000, in some cases. But reproduction size is severely limited for many of those.
My approach for higher ISO work is to use TAv mode, and let the ISO float as high as necessary based on my shutter speed and aperture settings. Those are non-negotiable aspects for me to get the creative results I want in terms of motion capture / movement blurring and depth of field. If I end up with one or more shots at ISO settings that are unusable because of that, so be it. It's no loss, since I couldn't have captured those shots any other way based on my creative requirements. My philosophy is, any shot that represents my creative vision is better than no shot at all. I can always choose whether to keep it or not