For your collection size, the data clustering option could be helpful for sure. Some things to keep in mind with using Data Clustering:
Data Clustering only works with the Rockset Column Index. This means that you would need to add
HINT(access_path=column_scan) to the end of the the FROM tables in your queries to leverage it (see this doc for more).
Data Clustering is a collection setting that must be set when the collection is created. If this is turned on for your org, the collection would need to be recreated to take advantage of Data Clustering.
Data Clustering must be set via the Collection Creation API (this doc for more). This means that any collection that would leverage Data Clustering would have to be created, via that API, with Data Clustering enabled, and you will need to specify the attribute that you would like the Data Clustering to be on (the API calls it the clustering_key).
Hopefully this helps. Let me know if you need anything else on it!