>>4136561Canon R10 + RF 800mm + 2x teleconverter gives a FOV of 2578mm, which is closer to the P1000 than the P900. This will also give you a lot better image quality.
Another option is an Olympus OM-5 with the 100-400mm lens (2x teleconverter included), giving you 1800mm and allows for high res mode (basically 80 megapixels so a lot of room to crop).
Both of these are much better for video as well.
