Thunderbolt 2, USB 3, Gigabit Ethernet, 4K Support, Firewire 800, Sound Ports
Mac Pro Westmere Performance with Handbrake Video Encoding
The 12-core is about 20% faster than the 6-core, because Handbrake uses only about 9 cores.
Beta build vs regular
The August 30, 2010 build is about 9% faster than the 0.94 release version.
These are the settings used for testing.