Your money, do you.
For me, I shot the Rokinon RF AF 14mm f2.8 and had no complaints with the AF.
So if the 85mm Rokinion is anything close to that performance of the 14mm version, I will much rather the 85mm f1.4 non-IS Rokinon over the f2 IS Canon especially considering the body has builtin IS.
Maybe if the body didn't have IS, my opinion may have been different.
If there isn't much price difference the Rokinon is my choice. But price is yet to be announced, so I await pricing.
Thanks MaX C for your reply and explanation.
Yes, you make a valid point that the R5 has IBIS, so the Canon RF 85mm STM's IS is not such a deal-maker.
I will definitely consider the Rokinon 85mm f/1.4 as an option. I have the Rokinon 12mm f/2 on my M5, and it is very good optically (but obviously a fully manual lens).