From what I've heard, AC: Odyssey tends to be a bit more CPU-limited than graphics card limited, possibly due in part to the DRM it uses. As WildCard said, if your CPU is what's limiting performance, then you might not get much higher frame rates from a graphics card upgrade.
Just checking on Youtube just now, I found a couple videos of people running the game on a GTX 1060, and they managed to get similar frame rates to what you describe, only at high settings, using recent mid-range CPUs like an i5-8400 or an i5-6600K. At low settings, they were pushing frame rates well above 60fps most of the time.