The Active Directory Maximum Limits and Scalability topic has been recently updated to reflect improvements in Windows Server 2012 to the number of RIDs that can be allocated over the lifetime of a domain. Another update was made to the section about maximum number of objects to reflect garbage collection batch size, which is 5000. Someone asked if it was advisable to increase garbage collection volume by increasing the size of the batches over 5000. And the answer from an AD developer was no, it's better to manually trigger the operational attribute dogarbageCollection=1 and garbageCollPeriod to speed it up. See the topic for more details and links to related articles.
This Active Directory Maximum Limits and Scalability topic was originally written by Kurt Hudson and has helped answer a lot of related questions over the past several years. Hopefully users will continue to discover it and find it useful