It depends on the size of the logs you intend to write. The Optane cache drive is rated at 100GBw/day, so if you write less than 100GB pf PFSense logs per day then it'd be fine (more, and you just reduce the overall lifetime before replacement).
Right but, the pfsense is new, I am consildating what was a bunch of iptables and snorts, Into 1, some were logged some we're not, now they will all be logged by 1 suricata, and pfsenses firewall. What I am saying is I don't yet know how much logs there will be, judging by the few that currently log, quite a bit lol.
That said, I don't know if Optane is really mature enough for the use, plus there is the endurance. I did find a very much up to the task gem. Intel DC S3520 150gb, 100 bucks, sata m.2, 415tbw endurance! With the best power loss protection on the market for an SSD from what I have read.
On the flip side, the Optane memory doesn't need PLP due to it's design, is cheaper, is good sized for purpose, and newer/faster. Also like you said 100gb of writes per day, it will be doing very very frequent logs, however will it do enough to use 100gbs a day, probably not. If it did, I would need a much much bigger SSD, or to move all to a syslog server anyway.
Tough choice.
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