I think you've likely encoutered that artifacts such as banding can and are often times dealt with by the RAW developer. However in other cases, its not so easy or possible and so you may notice banding appearing in certain images, and not in others at the same sensitivity.
On the other hand, the ISO51200 sample didn't exhibit any banding on my end using both RAW Therapee and Adobe Camera Raw(without NR). Though I still wouldn't recommend ISO51200 for anything but extreme measures given that the limited amount of detail available at this level.
Having said that, I did notice a significant magenta case in your table DNG. And at first glance(without looking) I'd say this was most likely due to underexposure. To which I'd add, one helpful tip I've discovered, is to lean to the right as far as possible without blowing highlights when shooting at higher sensitivities. Which helps reduce overall artifacts and more importantly... the type of problems such as the ones seen here.
Other than that, I'm happy to report that your sensor seems pretty much identical to my own in terms of high ISO performance. And so I'd say you are safe! and that there is no need to send out your unit as far as this goes. :)
FRT. here's some RAW Therapee/Topaz Denoise output from your ISO51200 sample. And while its not the greatest! - I'd say its good enough for emergency use if/when needed :)
PS. I used to shoot at max sensitivities with my K20's on a regular bassis. However, with the K-5, I've gotten into the habit of limiting my output to ISO2000. And that's not because I'm afraid of max ISO, but because I don't like the low level noise reduction that the K-5 applies to RAW files. Which kicks-in at ISO2200. And therefore, by keeping the meter bellow 2200, you can push process in post(RAW developer) and avoid the detail loss that comes with the K-5 prime engine. The downside on the other hand is that you have more noise to deal with(so its a give and take).
Anyways, based on what I've seen here, I'd say you're K-5 is in good hands! - Take care and thanks for participating.
Sincerely,
JohnBee
