To have a look at what's new in 9.6 see: https://wiki.postgresql.org/wiki/Newin96

Quick list of major features:

Parallel sequential scans, joins and aggregates

Elimination of repetitive scanning of old data by autovacuum

Synchronous replication now allows multiple standby servers for increased reliability

Full-text search for phrases

Support for remote joins, sorts, and updates in postgres_fdw

Substantial performance improvements, especially in the area of improving scalability on many-CPU servers