: Improved responsiveness when using GPU-accelerated tools such as the Blur Gallery and Lighting Effects. Exclusive "Extended" Features
Released in late 2012, the 13.0.1 update was primarily a stability and security patch: Security Fixes: Adobe Photoshop CS6 13.0.1 Extended Final Multilanguage
Even if you skip the Extended features, the core update from CS5 to CS6 was one of the most significant jumps in Photoshop history. Adobe Photoshop CS6 13.0.1 Extended Final Multilanguage