I'm just about to build a NAS with some leftover parts from an old upgrade, some new parts, and the disks out of my current NAS
7900X3D
64GB DDR5 (I'll probably run it at 4800MT/s)
4x 20TB HDD in ZFS Z1 (I have an off-site backup)
6.4TB NVMe (PCIe 4.0 x8) for L2ARC
1.92TB NVMe (PCIe 3.0 x4) for SLOG (maybe, not sure)
With the recent changes to L2ARC persistence and block size in TrueNAS, I intend to basically warm my L2ARC for a couple months, and then just basically never hit my disks again. My seeding torrents will probably fit entirely within L2ARC, as will a lot of my media library. In theory I get the benefit of a 52TB array with one disk redundancy, with the speed of NVMe for reads. I know SMB doesn't do sync writes, so my SLOG won't help there, but I have some VMs and containers using NFS shares which I think does? Normally so sync writes.