Here's some worthwhile info to keep in mind:
Focus setting only matters if you don't use the button. When not using the button, it refers to the percentile of the focal length that will be sharply focused (0 is essentially the lens surface, 100 is the most distant viewable point). To really appreciate how it works, try adjusting focus one increment at a time with aperture at 100.
Shutter speed setting only matters if the car is in motion.
Exposure/Color/Sepia should be adjusted based on lighting conditions (hence the presets, though they may not be ideal). Benja's photos of the Focus ST in his OP show how exaggerating color & exposure can work to create the feeling of a bright, sunny day.
Contrast & Brightness settings correlate very closely (though not at 1:1). While there are certain effects that can only be achieved at the extremes, it doesn't really matter whether you use 20/25, 50/55 or 70/75, the photos will look nearly identical as long as the ratio is similar.
Though the most realistic images will be at 1x (because it most closely replicates the human eye's perspective), aperture will need to be adjusted based on your focal distance & zoom. A higher setting is required to achieve the same depth of field effect at higher zoom levels, because zooming compresses distance.
Here are 2 photos I took to illustrate the principle (these are from Horizon 1). The cars are in identical positions. The top photo was taken from very close to the Evo, at 1x zoom and 35 aperture; the bottom one much farther away, at 5x zoom (if I remember correctly) and 70 aperture. You can see that with half the aperture; the depth of field is actually shallower (more pronounced) at lower zoom, and that depth-wise, everything appears much closer together at the higher zoom level.


The most important thing to remember is that low detail environmental textures are the biggest barrier to realism. If you want to fool an expert eye, be very aware of what you include in frame & use perspective+higher aperture to draw focus away from textures that are noticeably unrealistic. Don't forget about moving the watermark if would be less distracting in a different position.