Well, I just try the strategic map at 800x600. I can view a smaller portion of the map but it is much faster and easier to move unit icons when there are many of them in a small province. Battle field looks better at 1024x768 if your PC can handle it.

Strategic map: 800x600 for faster game play and easier control.

Battle map: 1024x768 (or higher) for the feel of the open space. Lower resolution wouldn't reduce the fun much.