PDF/X Colors: "Simulate Print Colors" vs "Screen Colors"

[Nostaw]

I noticed, when exporting PDF/X, the colors in Acrobat of the exported PDF document look different on having "Simulate Print Colors" or "Screen Colors" ticked. Aren't the colors suppose to always look the same in Acrobat, no matter if in Xara "Simulate Print Colors" or "Screen Colors" have been ticked while working and designing a document? I always thought these options are just for viewing colors but never noticed they incluence the output.

So my question is, before exporting to PDF/X should this option be set to "Screen Colors" or "Simulate Print Colors" when all colors in the document are set to CMYK? (Obviously "Simulate Print Colors" should be ticked, but I'd like to hear your thoughts).