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The K-5iis is a fine camera - a flagship-quality model, with excellent build quality, massive estimated shutter life, great IQ, and good high ISO performance. None of that has changed - everything you could do with it in late 2012 when it was released, you can still do now.
The K-70 is also a fine camera, but best described as mid-range. The build quality and shutter life are still excellent, but not quite to the standard of the K-5iis. Resolution has improved considerably, and that's nice. But the biggest improvement is in high ISO performance, and it really is very noticeable indeed. The question is, do you need that?
What do you shoot, where, and at what times of the day or night? Do you use mostly available lighting? Do you need high shutter speeds for creative control? If you think you're likely to shoot at ISO 6400 and above regularly, the K-70 will give far better results - no question. But if most of your work is at ISO 100 to 3200, the differences really don't matter so much - especially if you're processing RAW files yourself with good software such as Lightroom.
If you can acquire a lightly used K-5iis with low shutter count in excellent condition, and at a good price, it's a great choice - so long as high ISO isn't your top priority. If it is, though, or if the peace-of-mind a new camera (and perhaps extended warranty?) can offer, the K-70 might be a better choice