At this time no such grid or cheat sheet exists. There is a very simple reason for that - requirements vary on your usage, longevity, work load, and concurrency.
If you have a site where you are only really using it to dump files, then the CPU/storage requirements are likely very low. Conversely if you are hosting quizzes, using features such as Availability, and Completion, then those requirements will be much higher. If you have a large number of file submission assignments, and you are directly (not using a video service) hosting video then your storage requirements could be massive when you only have 100 users, but if you are only using features such as Lesson
, Forum, etc. then your storage requirements could be tiny for 10,000 users.
Additionally the TOTAL number of users is a not a particularly meaningful statistic. There are Moodle installations out there with millions upon millions of users which do not need massive specifications because the concurrency is low. Equally there are installations with extremely high concurrent usage but low total user counts. The total number of users _may_ increase storage capacity requirements, but that depends on what they're storing.
In addition you will find that many larger installations scale their load, at which point the number/type of processor, and the amount of RAM, become less meaningful again because they are on a number of different servers. Storage with these types of installation is largely SAN or cloud based so, again, it's really moot.
So there is no quick matrix of users to server requirements for the simple fact that it really depends on the nature of the workload, which is entirely dependant upon the client. You will find that many Moodle Partners
will discuss this with you in more detail and be able to advise after discussing your functional requirements.