I have a very high-end system (email@example.comGhz, 16GB memory, NVidia GTX-1080Ti w/ 11GB)
Fixed Resolution, borderless
Screen Resolution: Use Desktop Resolution
Mouse Cursor: Software
CPU Sleep Mode: Off
Memory Usage: 75% (fully to the right)
Max. Texture Size: fully to the right
No Winter Map: Off
Auto-save Turns: 12 - fully to the right (will use more disk space, but if you never turn your game back to previous turns, the default of 6 is more than enough)
Textures initialized: On
Smaller fonts: Off - on a large monitor I would recommend this, unless you like tiny text. You may have to try this out for your liking.
Tip: The game engine uses very old DirectX settings, and can often have issues when switching from the game to other windows apps through <Alt><Tab> while playing. In such cases you will get a DirectX error and the game will crash. This has nothing to do with your resources or game settings, only with the way the game uses DirectX. It generally only happens when there is some DirectX conflict, so it mostly depends on what app you are switching to.