Hey All - I have been a Pentax photographer since I was a kid and just supplemented my K1 II and K3 II with a K3 III.
The K3 III is awesome!
I have a lot of new and old Pentax lenses so while the idea of considering another platform (and mirrorless) for nature photography was tempting, I won some $ from work AND got a great deal on an Open Box K3 III from Adorama and went with it.
I have been using the K3 II with the 300mm for the extra reach, but quality was not as good as the K1 II for early morning low light shooting. So other option was K1 II - but 300mm (even with 1.4x) was not quite what I wanted as far as reach.
I have been out shooting early the last two mornings with the K3 III and a DA* 300 (and today with a 1.4x tele-converter) and am amazed at the image quality at high ISOs - aka 5000 and 6400. Still learning the camera but am excited to see how I progress! I plan to do some comparisons between the three cameras - but so far I am REALLY impressed.
A few shots attached - most are 4000 to 6400 - though a couple are 400 to 1000 ISO.
(You can see the originals here at higher res:
Prospect Park Birds )
Jonathan