Earlier this month I delivered some EXT4 vs. ZFS file-system benchmarks using the new ZFS On Linux release that is a native Linux kernel module implementing the Sun/Oracle file-system. Testing was done from a single disk configuration due to the available hardware within our labs and among Phoronix readers single disk configurations being most common.
A Phoronix reader wishing to show ZFS beating out EXT4 on Linux conducted his own tests from an IBM server system with Intel Xeon E3-1230 processor, 16GB of RAM, and a total of 22 disks. He was running Red Hat Enterprise Linux 6.4 with the Linux 2.6.32 kernel and tested EXT4 and ZFS.
Disk test configurations were ZFS with RaidZ in a JBOD configuration, ZFS in RAID 10, ZFS in a mirrored JBOD array, EXT4 with LVM in an MDRAID5 JBOD configuration, RAID with LVM in a mirrored mode, and then EXT4 with a hardware-based RAID5 array. With this testing, the ZFS On Linux configuration shined over EXT4.
Benchmark results in full for this high-end multi-disk configuration can be found on OpenBenchmarking.org. There's also this forum thread about the ZFS vs. EXT4 RAID independent testing and other details.