The Settlers - what a terrific game - I remember playing with a friend, splitting the screen along the centre with a piece of card. Great memories.
WinUAE has a powerful post-processing engine that can utilise either DirectX or OpenGL. I would suggest experimenting with the screensize/window size options in WinUAE, then enabling the DirectX/OpenGL filtering and changing the stretch/scale sliders. It is also possible to add extra effects to improve the quality of the display, whilst adding Scanlines will give the appearance of an old TV/monitor.
Good luck,
James
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