Owl at Dusk: EV and High ISO at 871mm

I found myself in unusual circumstances recently. This year an owl which I follow has returned to a different location which requires unusual settings for the shot.

First is the SOOC, and second is the shot PP'd to show the circumstances.

1) This is the SOOC shot I took using manual focus, in Program exposure mode, and dialling up the max ISO to 12800. It is handheld at 1/20th of a second at 871mm - pretty amazing VR / Image stabilization from this Panasonic Leica 100-400mm on the Panasonic G7. I had never taken a photo above ISO 3200, and even that only for ID photos, so this photo surprised me. (Playing with the shot in PP, I discovered that I should use minus EV some before rushing to raise the ISO.)

2) This is post processed down 1.5 stops to be (roughly) accurate to how I saw the owl. It was 5:30 pm, in a heavily canopied hammock, and in the shadow of what little light actually penetrated. I had to use manual focus due to the darkness. I typically shoot in Program mode and dial in a max ISO appropriate to the lighting, and typically only use EV to adjust for back lighting, or a white bird in the sun. In this case I used 12800 to get the camera to agree to shoot, but I should have first dialed in EV -1.3 and only run the max ISO up to 6400. Even better, might have been to dial in -1.7EV and use manual ISO at 4000 and 5000. I would have needed to add back the 1.5 stops in PP, but that would probably be better than getting the right exposure SOOC using such an high ISO. (Not to even touch the fact this is handheld at 1/20th of a second at 871mm EFL.)

Here is a link to the SOOC that keeps the EXIF, and offers the real original size image: https://flic.kr/p/NBoXG3