Sony 100-400 GM or Sigma 120-300 f2.8 Sport - help deciding

Since moving to Sony 6 months ago I have had a bit of a dilemma on long lenses for wildlife photography (deer etc rather than bif). I currently have a Sigma 120-300 Sport which is a great lens and incredibly sharp with near native af (as long as you don’t use tc), however it is also very heavy. Sony then launched th 100-400 GM which is very tempting as it is 2kg lighter and could also take tc’s better.

Has anyone any experience of shooting both these lenses on Sony, and what would I be missing other than the obvious of the faster aperture (Sony handles iso far better than my 5d3).

Btw I am using the Sony A7Rii

Tia

I've never shot the 120-300mm, but have seen tons of amazing images with it here on POTN and Flickr. I do (presently) own the 100-400mm GM and regard it as pretty amazing. Based on what I do know here are my thoughts:

1. The 120-300mm with it's f/2.8 aperture comes at a (literally) very heavy cost. 7.47 lb (3.39 kg) is way too oppressively heavy a lens for my interest and realistically becomes very limited use for handheld photography. A monopod or tripod would be requisite for most shooting imo.
2. Although it's labeled 120-300mm it has been documented pretty well that it's only about 270mm at the longest end. Not a huge deal, but this multiplies when you add a 2x and it's only 540mm and not actually 600mm. That said, I don't know what the 100-400mm GM's longest actual focal length is - whether it is actually 400mm or close to it.
3. 120-300mm has a beautiful bokeh for a zoom - the 100-400mm GM can't touch that.
4. The 100-400mm GM is insanely sharp, on par with the massively expensive (and heavy) Canon 200-400L.

I absolutely can understand the appeal of the 120-300mm, because it delivers wonderful images. But for me this is an easy choice because the sheer weight of the 120-300mm with the adapter makes it a very unpleasant lens to actually use in practice. If it's not enjoyable to use, then I am much less likely to use it.

David Arbogast wrote in post #18494189
I've never shot the 120-300mm, but have seen tons of amazing images with it here on POTN and Flickr. I do (presently) own the 100-400mm GM and regard it as pretty amazing. Based on what I do know here are my thoughts:

1. The 120-300mm with it's f/2.8 aperture comes at a (literally) very heavy cost. 7.47 lb (3.39 kg) is way too oppressively heavy a lens for my interest and realistically becomes very limited use for handheld photography. A monopod or tripod would be requisite for most shooting imo.
2. Although it's labeled 120-300mm it has been documented pretty well that it's only about 270mm at the longest end. Not a huge deal, but this multiplies when you add a 2x and it's only 540mm and not actually 600mm. That said, I don't know what the 100-400mm GM's longest actual focal length is - whether it is actually 400mm or close to it.
3. 120-300mm has a beautiful bokeh for a zoom - the 100-400mm GM can't touch that.
4. The 100-400mm GM is insanely sharp, on par with the massively expensive (and heavy) Canon 200-400L.

I absolutely can understand the appeal of the 120-300mm, because it delivers wonderful images. But for me this is an easy choice because the sheer weight of the 120-300mm with the adapter makes it a very unpleasant lens to actually use in practice. If it's not enjoyable to use, then I am much less likely to use it.

Thanks David. Totally agree on the weight, the Sigma is a beast. Tbh that is one of my big reasons for changing, however as you say the bokeh etc is very good