Alright, some more data. I'm using freenas for 10 years (or so) now, however to my knowledge only on AMD CPUs. Managed to get bhyve up and running, had quite some issues (AHCI vs VirtIO drive issue the last one, all solved by end of last year). VM was not screaming fast but snappy enough to do everyday work if required. One strange thing with the on-board NIC (something with MSI-X interrupt routing...) worked around by putting an intel e1000 PCI card in. Now I wanted some more RAM, meaning a new old Mainboard with 32GB on it was in order.
Two choices:
1. ASUS PRIME B-350M, Ryzen 7-1700, 32GB DDR4, 6x SATA3
2. ASUS P8Z77M-Pro, i7-3770s 32GB DDR3, 4xSATA2, 2xSATA3, 2xeSATA
I go for the newer one, everything goes up, re-assign the NIC (the onboard one works, PCI doesn't fit on this board), fast and snappy VMs with more RAM if desired, more CPUs if desired, smiles all around. But... every morning the whole server is in some sleep mode and doesn't want to wake up. Checked all APM settings, googled, to no avail, except that there are some APM issues with B-350 chipset. Dead end for now.
Reassembled into the other case with the intel board, re-mounted all the six hard drives (sheesh), fired up, all came up instantly. Except... the VMs are slow as molasses now. I mean really slow, like described in this thread above. Tried to switch off the Meltdown/Spectre mitigations to eliminate degradations... no change that can be felt.
Current version is FreeNAS-11.3-U4.1. On AMD no issue with VM.
Conslusion for now: FreeNAS on intel is possible, but Win10 VMs are a waste here. Slooooowww. Now I need to go for another board.... For now, the one VM I need, is transplanted to a Hyper-V via viBoot. Almost as fast as the host machine now.