Rome 2 Performance Tweak for Modern Systems

Go to C:\Users\Your Username\AppData\Roaming\The Creative Assembly\Rome2\scripts and open preferences.script

Change gfx_video_memory from 0 to -4000.

Change number_of_threads to your CPU threads (you can find this in Task Manager under Performance > CPU > Logical Processors) (in my case it was 16).

Save the file.

Game runs far better after this.