Major Description
stillalex, as discussed I think there is some room for improvement when running a user query with QueryBuilder.setScope(String groupId, boolean declaredMembersOnly), where declaredMembersOnly is set to true. Instead of resolving the member references and comparing the authorizableId in order to filter out those that are not declared member of the given group, it would be sufficient to compare the contentIDs and thus avoiding the extra round trip resolving the UUID to a Tree and building the corresponding Authorizable.
I will attach a patch illustrating the proposed improvements along with some extension to the corresponding benchmark (and some initial numbers).