CAGI is an acronym for Compressed Air And Gas Institute.
This U.S. based organization appears to be a 'for profit' company that provides on-line information relating to compressed air and gases. To obtain these services it's necessary to subscribe from their home page.
They also publish a set of compressor definitions which, if compressor manufacturers provide the appropriate information, makes it easier for individuals to compare offerings from different compressor companies.
As you travel the web looking for data on compressor manufacturers, you will see that some of them offer a CAGI fact sheet regarding their individual models. If you are able to get CAGI sheets from a number of firms, it should make it easier to compare "compressor to compressor". It appears as though the compressor manufacturers do not charge for the CAGI comparison sheet.
I don't subscribe, so I can offer no comment on the value or efficacy of their data or service.
www.cagi.org is the CAGI web site