Need advice choosing next lens

So I got an OM-1 a few weeks ago and I love it. I have been using it to take pictures of large and small birds. I have been doing this primarily with the m.zuiko 40-150 4-5.6.

Generally when taking pictures of smaller birds i use the digital teleconverter to get the shot i want and then crop to match in lightroom afterwards.

I was curious what people think about when considering upgrading their lenses for this use case. There are two main options i am looking at. The first is to get the Olympus 75-300 or panasonic 100-300. The panasonic seems to be better and more expensive. In that same price range is the m. Zuiko 40-150 f4 pro.

Obviously the longer focal length would capture more detail. On the other hand the increase in sharpness and aperture size of the pro would probably provide a lot of image quality and be much more useful at lower light.

Thanks for the advice!