For best performance in RabbitMQ, follow the advice of its creators. From the RabbitMQ blog:
RabbitMQ’s queues are fastest when they’re empty. When a queue is
empty, and it has consumers ready to receive messages, then as soon as
a message is received by the queue, it goes straight out to the
consumer. In the case of a persistent message in a durable queue, yes,
it will also go to disk, but that’s done in an asynchronous manner and
is buffered heavily. The main point is that very little book-keeping
needs to be done, very few data structures are modified, and very
little additional memory needs allocating.
If you really want to dig deep into the performance of RabbitMQ queues, this other blog entry of theirs goes into the data much further.