These are vulnerable to Meltdown, and the page table isolation patches are required to secure kernel memory. These do involve a performance hit, so I'd recommend Core-2 Quad 9550s as an upgrade for a minimally-usable machine.
However, these are not SMT/hyperthreaded, so many of the Specter vulnerabilities do not apply.
OpenBSD runs well enough on them, and these machines are likely what I trust most with this OS.
Most Linux runs on these machines (RedHat 9 doesn't - requires an i3), but will pause on the mei_me module and look for a response from the ME that you have lobotomized; blacklist the related modules if you want to boot faster.
However, these are not SMT/hyperthreaded, so many of the Specter vulnerabilities do not apply.
OpenBSD runs well enough on them, and these machines are likely what I trust most with this OS.
Most Linux runs on these machines (RedHat 9 doesn't - requires an i3), but will pause on the mei_me module and look for a response from the ME that you have lobotomized; blacklist the related modules if you want to boot faster.