I'm not an expert photographer; I admit that. I consider myself more of an advanced amateur. So for what it's worth, here are some K-5 test shots using progressively higher ISOs via the "Sv" (sensitivity) setting on the dial. I decided, based on these shots, that for acceptable clarity, I'm not going above 6400 in the future. That's me. You may have different standards. These were shots taken of a pruning tool on my back porch, for lack of a better subject at the time.
At any rate, here goes, starting with ISO 400:
ISO 800:
ISO 3200:
ISO 6400:
ISO 12800:
ISO 25600:
ISO 51200:
OK, now to get away from experimentation - here's a "money" shot taken of a Smith & Wesson Model 27-2 made in 1978. I took it in a shaded area at ISO 160, 1/100 sec, f8, at 35 mm using the 18-55mm kit lens that came with the camera. Cropped and processed in Photoshop Elements 7. I think it turned out pretty well. One thing I discovered is that at 16+ megapixels, closeups of anything reveal even specks of dust!
Hope you'll find these K-5 pictures interesting/useful.
John