The verdict

CPU
GMKtec NucBox M5 has 1.2x the CPU throughput (19,000 vs 16,359 PassMark).
Plex
Dell OptiPlex 7000 Micro transcodes more 4K HDR streams (~5 vs ~3).
Idle power
GMKtec NucBox M5 idles lower (8W vs 10W) - cheaper to run 24/7.

Which wins for each job

Job Dell OptiPlex 7000 Micro GMKtec NucBox M5
Plex / Jellyfin ~5 streams win ~3 streams
Frigate NVR ~4 cameras win add a detector
Proxmox / VMs 16,359 PassMark 19,000 PassMark win
Firewall / router 1 NICs 1 NICs
Local AI / LLM no slot no slot

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 7000 Micro GMKtec NucBox M5
Price (list) $330 $329
CPU Intel Core i5-12500T AMD Ryzen 7 5800U
Cores / threads 6 8
PassMark 16,359 19,000
iGPU Intel UHD 770 Vega 8
NICs 1 1
NIC model Intel I219-LM Realtek RTL8125
RAM max (GB) 64 64
M.2 free 0 2
PCIe slot none none
Idle (W) 10 8
TDP (W) 35 25