Tuning postgresql.conf when benchmark
Yes, you can run those queries in pgbench. Look for the parts talking about custom scripts:


http://www.postgresql.org/docs/9.4/static/pgbench.html


The max_connections, and shared_buffers seem really high for the server you have. 25% of RAM for shared_buffers would be more reasonable, and getting a connection pooler like pgbouncer to handle lots of connections would be much more productive. 


You might find this useful as well:

https://wiki.postgresql.org/wiki/Tuning_Your_PostgreSQL_Server

Hope that helps. =)