Of the many new features for Linux 3.12, EXT4 has aggressive extent caching and other notable changes. Samsung's Flash-Friendly File-System (F2FS) meanwhile also has small features and performance improvements.
Proper tests of the Linux file-system improvements in 3.12 will come once the kernel is close to being stabilized, but as an early performance preview, here are some benchmarks of EXT4 and F2FS from Linux 3.11 and Linux 3.12 Git 20130910 from the System76 Gazelle Pro laptop. The laptop was tested with its Intel Core i7 4900MQ CPU and Intel 520 Series 120GB SSD.
The stock mount options for EXT4 and F2FS were used throughout testing. While the EXT4 and F2FS changes in Linux 3.12 are only evolutionary, in a few tests we were able to see some change in performance. To explore these early Linux 3.12 file-system benchmark results, on OpenBenchmarking.org visit 1309118-SO-LINUX312F51.