PostgreSQL Performance - Many Large Databases

I run an internal (development) database server containing 25 databases each ~71GB in size. There are usually between 50 and 100 active connections at any given time. What can I do to help improve performance other than upgrading the server hardware (which unfortunately is not an option at this time)?

Server Specs

8x Xeon E5450 @ 3.00GHz
16GB RAM

postgresql.conf

max_connections = 128
shared_buffers = 4GB
work_mem = 32MB
maintenance_work_mem = 1GB
fsync = off
full_page_writes = off
wal_buffers = 16MB
checkpoint_segments = 32
checkpoint_timeout = 15min
checkpoint_completion_target = 0.7
effective_cache_size = 12GB
default_statistics_target = 100
autovacuum = on

Largest Tables

These values are the same for each database.

6239 MB
4078 MB
3757 MB
2365 MB