The verdict

CPU
Lenovo ThinkCentre M920q Tiny has 1.5x the CPU throughput (7,728 vs 5,307 PassMark).
Plex
GMKtec NucBox G2 transcodes more 4K HDR streams (~5 vs ~3).
Idle power
GMKtec NucBox G2 idles lower (6W vs 10W) - cheaper to run 24/7.
Networking
GMKtec NucBox G2 has more NICs (2 vs 1) - better for a firewall or VLAN trunk.
RAM ceiling
Lenovo ThinkCentre M920q Tiny takes more RAM (64GB vs 12GB).
Local AI
Lenovo ThinkCentre M920q Tiny has a PCIe slot for a low-profile GPU - the other needs a DIY build for local LLMs.

Which wins for each job

Job GMKtec NucBox G2 Lenovo ThinkCentre M920q Tiny
Plex / Jellyfin ~5 streams win ~3 streams
Frigate NVR ~4 cameras ~4 cameras
Proxmox / VMs 5,307 PassMark 7,728 PassMark win
Firewall / router 2 NICs win 1 NICs
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 GMKtec NucBox G2 Lenovo ThinkCentre M920q Tiny
Price (list) $159 $150
CPU Intel Processor N100 Intel Core i5-8500T
Cores / threads 4 6
PassMark 5,307 7,728
iGPU Intel UHD (24 EU) UHD 630
NICs 2 1
NIC model 1GbE (chip unlisted) Intel I219-V
RAM max (GB) 12 64
M.2 free 1 1
PCIe slot none x8-lp
Idle (W) 6 10
TDP (W) 6 35