I was about to recommend OP to check used Threadripper 1st gen, even the 8 core should be enough (I really loved the 8 core with so many PCI-E lanes). Let us look at his requirements from what he has said:
- Virtualization with IOMMU
- NAS
- HTPC
- 2 GPU slots + add one for the host (maybe unless he runs the host OS headless with something like Proxmox)
- at least 8 Sata ports or enough PCI-E slots for expansion
- maybe have a slot for an Optane write cache
If the price is not too high for the Xeon build, the power consumption shouldn’t be too different from the Threadripper (actually, should be a little lower). But there is a case to be made about TR with OP already owning DDR4 RAM (albeit not ECC).
@Airstripone if it warms you up to know what I’m running right now (don’t start laughing), I have been fine with a Pentium G4560 with 8 GB of DDR4 (obviously non-ECC), a GT1030, 1 PCI-E ssd, 1 sata ssd (passed), 1 USB 3.0 adapter (passed) and 2x 1 TB HDDs, with a 350w bequiet PSU. I’m running Manjaro as host OS, Win10 as guest with the 1030 passthrough and 3 GB of RAM for it. I’ve been struggling lately because of the CPU and RAM.
A TR 1900x should probably fit your requirements just fine. Start looking for 1st gen Threadripper deals, maybe even CPU+mobo combos. I really don’t think a consumer motherboard (maybe except x570, but it’s expensive AF for not many benefits except a newer CPU) would help you with your requirements. Used servers will probably be more expensive than a 1900x build, unless you manage to get an absolutely insane deal.
As a side note, I’m trying to get out of pci-e passthrough and running 2 OS on 1 box, because of the low-end hardware (it was really fun while it lasted though), now I have 2 racked PC, looking to build a 3rd one, all powered on 24/7. I don’t have enough $$ for a high-end build, but if I would afford it, I’d definitely go for a TR1900x and fill its expansion to the brim.
Edit: both my PCs are low-power consumption, the other one having an Athlon II x2 and a 6670 and where I live electricity is really, really cheap, so I don’t pay a lot on my bills. The 3rd one I would like to be something like an i3 or an even lower-end Pentium (I already have some 8 GB DDR3, a sata SSD and a rack-case lying around).