Currently testing with Debian to get a handle on things and what drivers are needed.
Installed r8168-dkms and firmware-realtek. The NICs run without either, no matter what the dire warning suggests.
iperf3 at 940 Mbps, which is basically the throughput limit of GIgE, from what I understand. Routing and/or VPN not yet tested.
lm-sensors detects and reads (here at idle, without fan)
Adapter: SMBus I801 adapter at f040
fan1: FAULT (div = 8)
temp1: +42.5°C (low = +0.0°C, high = +85.0°C)
temp2: +42.5°C (low = +0.0°C, high = +85.0°C)
temp3: +42.9°C (low = +0.0°C, high = +85.0°C)
Adapter: ACPI interface
temp1: +45.0°C (crit = +95.0°C)
Adapter: ISA adapter
Package id 0: +45.0°C (high = +105.0°C, crit = +105.0°C)
Core 0: +45.0°C (high = +105.0°C, crit = +105.0°C)
Core 1: +45.0°C (high = +105.0°C, crit = +105.0°C)
Core 2: +45.0°C (high = +105.0°C, crit = +105.0°C)
A fan is definitely needed if you're going to push it hard.
I stopped when the CPU temp crossed 75°C
I'm using a Noctua NF-A9. Running tests on 12 V to start, as I don't have an adapter from the non-standard fan connector yet. I'll try at lower voltages as well. I haven't checked for an EMC2103 driver yet in the OpenWrt tree/packages, though there is one in upstream Linux. BIOS is another option, though I like to run as quiet as I can.
Looks like even 5 V on the Noctua NF-A9 is enough (~67 °C), though 7 V is better (~64 °C).
Note to anyone reading this in the future -- the schematics suggest that it is a 5 V fan that is needed to run off the on-board connector -- to be confirmed