I still struggle to find the best settings to get the best possible, the least jumpy video. I've tried many fps, ISO and shutter speed combinations and the viewfinder always look very jumpy.
chdkptp live view has significant limitations, it's not going to great in the best case.
Most of this won't be affected by shooting settings. In very low light, the frame rate on the camera will probably be lower.
It looks like the current sx260hs port will suffer especially low frame rate in video mode or when recording video. I can post a test build for this if you tell me which canon firmware you have.
As for the Canon analog video adapter - is it possible to use also a USB to HDMI adapter for connecting the camera to a PC? Will I get a stream on in this way? Lag is no problem.
Like most powershots, SX260HS does not support HDMI out in shooting mode, and we have not found a way to override this.
You can use a NTSC/PAL analog video capture adapter (something like https://www.amazon.com/EasyCap-Capture-Video-Adapter-Converter/dp/B01H6OQI1W
if you want to be cheap) with an AVC-DC400 compatible cable, but that will only give you SD resolution. For general webcam use, spending the same money on a dedicated webcam would probably be a much better option.