We haven't done any formal benchmarking, so there are no "official numbers".
Specifically regarding the question on number of users, we have systems with hundreds of users worldwide, many of them heavy users.
From our experience, in large enterprise systems, the bottleneck is usually the database rather than the application (as long as it is properly built).
If you have any specific question, we will try to answer it.
(Pawel - Any insights since you asked your question two years ago?)
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