l3l3l5l: I found that fantastic article about antiquated display modes on
nerdlypleasures Blogspot blog. And It appears that some game designers took into account stretching of the graphics for 4:3 displays and some didn't. In the article they compare screenshots from Elite Plus (correction not taken into account) with Loom (correction taken into account).
One easy way to check this is to try to find a rounded object in a game and use the mode in which the object looks round rather than oval. In case of Populous I it's the earth icon in the bottom right corner of the screen - it's only round when you use 16:10 modes without 4:3 aspect correction.
Personally, I hate when games are being upscaled from 320x200 to 320x240 by DOSBox. As far as I understand all pixels were stretched vertically evenly instead of being interpolated as you see in DOSBox. Have no idea why this has not been addressed yet, apparently this doesn't annoy anyone, but it would be great if someone developed more elaborate DOSBox algorithms as well a library of game modes which need aspect correction and which don't. I would even go as far as emulating the way old monitors worked with light traveling all the way from the tube to the coloured pixels, you know, that effect which gives you a warm retro blur. Pretty sure that's possible with modern graphics cards.
For games that didn't take vga mode 13h's 5:6 pixel aspect ratio into account, you can tell dosbox not to correct the aspect ratio in the configuration by setting aspect=false in the [render] section.
To correctly show content that took the pixel aspect ratio into account without scaling artifacts you need a display resolution of at least 1600x1200 ( 320 * 5 ->1600; 200 * 6 ->1200 )