Phoronix did a much more thorough comparison recently:
FreeBSD ZFS vs. TrueOS ZoF vs. DragonFlyBSD HAMMER2 vs. ZFS On Linux Benchmarks - Phoronix
As just one data point, I did a quick comparison of stat() calls
ZFS vs EXT4 on Debian Buster alpha4, on a DL380p.
I chose Debian buster because their contrib repo has zfs 0.7.12.
With a directory tree holding 480,000 files:
time find . -ctime 1 >/dev/null
EXT4: real 0m1.930s user 0m0.431s sys 0m1.493s
ZFS: real 0m3.326s user 0m0.495s sys 0m2.825s
EXT4 and ZFS were each on a single 10K WD3000BLFS SATA drive on
a HP P420i controller, in raid mode, as a single drive raid0 volume.
Even though the newer hpsa driver handles the P420i, you can still
get smart data via "smartctl -a -d cciss,0 /dev/sdb".
I think my results are fairly consistent with what Phoronix shows.