FreeBSD 4.x was considered by many as the most stable FreeBSD ever. Mainly because there were 11 point releases of fixes and enhancements (4.11), as opposed to today where FreeBSD major version only have 3-4 point releases. https://www.freebsd.org/releases/
It was not only the most stable, but for many applications, especially in networking, it was also the fastest single-threaded operating system, beating easily Linux and Windows XP or 2000. Unfortunately for FreeBSD, the launch of the Intel Pentium 4 with hyper-threading in 2003, then of the AMD dual-core CPUs in 2005 have made quickly FreeBSD 4 completely obsolete. The smaller FreeBSD team has required many years unt…
20 years ago it was unfortunately not unusual to experience the Linux "nuclear fsck" where it scrolls by so fast and for so long you know it's toast.