The verdict

CPU
Dell OptiPlex 7020 Micro has 5.7x the CPU throughput (22,934 vs 4,000 PassMark).
Plex
Dell OptiPlex 7020 Micro transcodes more 4K HDR streams (~5 vs ~4).
Idle power
Dell OptiPlex 7020 Micro idles lower (9W vs 16W) - cheaper to run 24/7.
Networking
QNAP TS-664 has more NICs (2 vs 1) - better for a firewall or VLAN trunk.
RAM ceiling
Dell OptiPlex 7020 Micro takes more RAM (64GB vs 16GB).
Local AI
QNAP TS-664 has a PCIe slot for a low-profile GPU - the other needs a DIY build for local LLMs.

Which wins for each job

Job Dell OptiPlex 7020 Micro QNAP TS-664
Plex / Jellyfin ~5 streams win ~4 streams
Frigate NVR ~4 cameras ~4 cameras
Proxmox / VMs 22,934 PassMark win 4,000 PassMark
Firewall / router 1 NICs 2 NICs win
Local AI / LLM no slot PCIe GPU slot win

Approximate - capacity estimates from curated specs, the same logic as the recommender. Verify against your exact setup. Prices move; check the retailer.

Full specs

Spec Dell OptiPlex 7020 Micro QNAP TS-664
Price (list) $750 $799
CPU Intel Core i5-14500T Intel Celeron N5095
Cores / threads 14 4
PassMark 22,934 4,000
iGPU UHD 770 Intel UHD (16 EU)
NICs 1 2
NIC model Intel 1GbE Intel I225-V
RAM max (GB) 64 16
M.2 free 0 2
PCIe slot none x4
Idle (W) 9 16
TDP (W) 35 15