I'm using a RTX 2070 Super, I have the graphics setting set to "High", and resolution set to 2560 x 1440 (I have 4k monitor).
I track my frame rate over longer periods using Razer Cortex, and my average frame rate is 57 fps over a period of 10 hours, 45 minutes and 12 seconds. What causes a big performance hit is fire in buildings. My minimum frame rate is 27 fps due to exactly this.
It feels to me like the game is putting out 60fps almost all the time (max refresh on this monitor), and the performance hit of burning buildings that is causing that drop to 57 average.
I have a number of issues with Odyssey, but performance isn't one of them. Please don't interpret that as me dismissing problems other people encounter - just want to say, its working very well for me with absolutely no tweaking or messing about.