How is panasonic's 4k photo mode low-light performance when compared to simple jpg 4k-resolution still?
4K will always miss out compared to a RAW still as there is so much more data that you can recover from RAW. With 4K the camera has already done the majority of processing in camera. However, I have used 4K to capture individual motion frames in relatively low light with reasonable results ... but it depends on what YOU define as reasonable!
This 4K image was taken from a 4K video shot on a dull, grey November day!