Carrying out 32 threads of 32MB writes, the fastest file-system was once again EXT4 on Ubuntu followed very closely by Btrfs and then came ZFS. Aside from the first test with Gzip compression where ZFS failed to outperform UFS+S/UFS+J, in the rest of the tests so far ZFS is certainly faster than the longstanding UFS competition.
When increasing the write size from 32MB to 128MB but sticking with 32 threads, Btrfs managed to outperform EXT4 by about 15%. ZFS meanwhile still handily beat out the UFS competition -- the Sun/Oracle ZFS was 53% faster than UFS+S and an impressive 2.68x faster than UFS+J.
Finally, at last, ZFS managed to outperform both EXT4 and Ubuntu. With the 32MB random write performance at four threads, ZFS was about 25% faster than Btrfs. EXT4 really struggled with this multi-threaded random write test where it was actually slower than UFS+J and just marginally faster than UFS+S.