Hey. Thanks for your quick response.
In terms of expected result, I think it would be down to the display card if you switched to a 4:3 resolution on a 16:9 or 16:10 monitor; you would get the black bars either side of the display like you do watching old TV programs on new TVs.
Whether or not you could even have that resolution, again, would be entirely card/driver specific.
I may be approaching this the wrong way but to give some context - if I want to draw 4 cards across the bottom of the screen as GUI components, I could make an image where each card is, say, 180px wide x 240px high. On an 800x600 screen, with a bit of spacing / margin, I can align these to use the full screen width. If I switch to full screen mode on a 4K monitor, they now only take about a quarter of the screen width. By switching the resolution, it maintains the same screen dimensions.
I saw the enableResolutionScaling but it didn't appear to scale my GUIComponents. I wasn't sure if this just effected the environment entities.