Is there something timing wise that will ensure that all 12,000 users hit the database in the same second? Because just spreading that load over 12 seconds drastically reduces the load to 1000 requests per second. If you had 12,000 human users that are not making requests 100% of the time you would be hard pressed to ever get them to all make a request simultaneously. Automated users are a different story but you still might be able to schedule them around each other.
I would guess that if one AOLServer machine can handle 1000 requests per second then 12 AOLServer machines should handle 12,000 requests per second. That says nothing about the database server though.
