It RF 70-200 f/2.8 worth it over f/4 for animals and potraits?

Hello guys,

I want to ask for help with what I think is GAS.

I am shooting animals in zoos and portraits. I currently have 70-200 f/4, which I like really much. I bought it quite cheap and used it a lot since.

But as GAS creeped in, I was thinking about getting 2.8 for more subject separation and more "pop" in portraits. The f/4 portraits look mediocre and with animals, I am able to hit ISO levels like 6400 and 12800 in pavillions when trying to freeze action.

I was offered some money for f/4 if I buy 2.8. But it is not that much money I was expecting, basically half of what it costs new now. Plus I would have to add 1400 EUR to buy 2.8.

My brain is saying NO, but GAS says - get it. I am divided, the money must mean the 2.8 is better, but I just don't see it. The reviews showing photos show pretty much same blur and separation at 200mm. The ISO will be half, yes, but will it save me going from 12800 to 6400? I get around 1/400 at ISO 12800 and going to 6400 is not that plus, maybe going to 1/800 is, but I will be there with 12800 anyway.

I have it paired with 24-70 2.8 where I got it to shoot stars at wide end, so there I knew I want 2.8. Here, I just don't see it.

Am I thinking it right? Where is the point of 2.8? If I don't see it, does it mean I don't need it? Will pairing 70-200 f/4 with something like 85 1.4 make more sense for portraits? Or is it all GAS?

Please talk me out of it XD

Thank you for help.