Well they're unlikely to be at max power draw. The moral of the story is use your old crap until it dies instead of replacing functioning equipment with more enviornmentally friendly things- supposedly this rings true for cars also, meaning it has less of a CO2 impact to drive your beater toyata corrola into the ground then it does to buy a new EV, so I've read.

I think the most important element is longevity, and for that you need passive cooling that stays under 50-60 degrees Celsius at full blast. You also need disk solutions that are easy/cheap to replace and sturdy. That means old SD cards (SLC or MLC in that order) or old SSDs at ~65nm with 100.000 writes per bit. Modern NAND only has 10.000 WPB.

I still have my 45 nm Atom D510MO running 24/7 since 2010 in a passive heatpipe+sink case and 14 nm NUC + Atom 8-core in Streacom passive cases since 2014 and 2021 respectively. I'm waiting for the SSD in the NUC to fail. The recent Atom runs on X-25E that I know will outlast me.

N100 is 3x the performance per watt of the Raspberry 4, but it also costs 3x. I prefer the lower cost of the Raspberry 4 that allows more redundance even if that means more "garbage" has to be manufactured until that redundance is applied. Combined with cheap heatsinks and SD cards I already have.

The low power server of excellence is the Raspberry 2 at 2W TDP; I can have that running on solar only with a 100Ah battery bank... I think it would stay on a week without sun. The only 32-bit ARM multicore processor with vanilla linux that will ever exist for eternity, with the reduced complexity that brings!