Understand that the IMAC screen may only meet sRGB standards. does this mean that proofing/editing with adobeRGB is irrelevant as it will not be displayed?
Therefore a professional monitor is still required?
does anyone know how to find out what standards a monitor does meet? (without reading manufacturers sheets?(which are not always easy to interpret))
If your display's gamut is only sRGB, then there is the possibility that you will not be able to display some colors from an image if they exceed the gamut covered by sRGB but are encompassed by Adobe RGB. Just in case, you can think of gamut like range. For example, sRGB may be have a range of 5 to 15 and Adobe RGB has a range of 2 to 20. This would mean a color such as 3 would exceed the range of what can be represented with the sRGB transformations.
To analyze the gamut covered by a monitor, you can use the ICC profile. Apple's built-in ColorSync Utility can be used for this purpose by first selecting the profile of the device, selecting "hold for comparison" using the down-pointing triangle near the upper-left of the graph, and then selecting a profile such as sRGB.
This isn't an issue of standards so much as it is of capabilities. Even the same monitor will have performance that generally worsens as it becomes older. If you regularly generate profiles you can track this decline in performance over time.