When it came to running an 8GB write test with IOzone using 4Kb block sizes, the only configuration that was slower than KQ Infotech's ZFS configuration was ZFS-FUSE. XFS, Btrfs, and EXT4 on both the 2.6.32 and 2.6.37 kernels were noticeably faster.
When switching the 8GB write test to using 64Kb block sizes, ZFS-FUSE performed much better, and the KQ Infotech / LLNL ZFS implementation was faster relative to the native Linux file-systems, but still it was of little competition. The fastest file-system continued to be Btrfs.
Testing out the 8GB read performance with IOzone, ZFS on Linux was actually faster with its reads here than EXT4 and XFS, but was slower than Btrfs.