Michael Larabel of Phoronix has reported some benchmarks from FreeBSD ZFS and TrueOS ZFS along with various open-source distros DragonFlyBSD, Ubuntu, and Clear Linux. In addition, he also provided some charts on the Meltdown Kernel page-table isolation (PTI) mitigation on various BSD and Linux distros. You may see the detailed report at the links below.

Some DragonFly HAMMER2 / FreeBSD ZFS / Linux EXT4 Benchmarks | Discussion
https://www.phoronix.com/scan.php?page=news_item&px=Meltdown-BSD-Linux-Compare | Discussion