edit: If creating an artwork with unknown destination but knowing that it will be printed on different CMYK printers which are not yet specified in the job, is it better to create in RGB or CMYK color space if the goal is creating design that will contain the most saturated colors possible in each eventual CMYK color space?
Another question that will hopefully help me understand. Is it possible to find exact color match of the example values from my first post if they are used separately one by one? Like an image with one flat color only. I thought that a wider color space encompassing a narrower color space can match all colors of the narrower color space. Is this not true?
I think the best things you can do are:1) Work in ProPhotoRGB so these gamut extremities aren't clipped2) Assign colors in your ProPhotoRGB file by using the CMYK values in the color picker. 3) Look at the CMYK values in your info palette while working in your RGB file.4) Use the newer "WebCoatedSWOP2006Grade3.icc" profile instead of the older "USWebCoatedSWOP.icc" for your RGB to CMYK conversions. They are much better.5) Make sure your Color Settings are setup using your preferred CMYK space and conversion options as these are used not only for the conversion but also for the CMYK values presented in the Info palette while working on an RGB file.This will help minimize, but not eliminate, the discrepancies you are seeing.Hope this helps!
The test show that the wider the color space the worse the color match. I don't know what to think about this but using wider RGB color spaces for a CMYK destination doesn't seem very attractive.
I'm afraid you might be getting caught up in the technical nitty gritty here. The bigger question is "What are you doing?" What's leading you to these questions? Are you working with photographic imagery or non-photographic content?