Claudius from ArangoDB here. Frank already answered a question about realtime queries below: "We are evaluating various possibilities, how to implement streaming queries in an efficient and scalable way. For instance, are restrictions to the general AQL necessary for such queries to be able to scale? Stay tuned."

Regarding performance, it would be great if somebody with excellent knowledge about rethinkdb would contribute to https://github.com/weinberger/nosql-tests