Phoronix has done a plethora of benchmarking tests highlighting performance differences between FreeBSD, Linux, TrueOS, DragonflyBSD. The author measures things like ZFS on FreeBSD vs ZFS on Linux and HAMMER2, networking performance, and others. Also, the Phoronix Test Suite has been updated to 8.6-M3. Check out the following links to look at the benchmark results.
Phoronix Test Suite 8.6-M3: https://www.phoronix.com/scan.php?page=news_item&px=Phoronix-Test-Suite-8.6-M3