I've only done all this work and research because I respect you and was genuinely interested in putting some science behind our use of 3D printers. You don't have to be mean about it. :(

You started with the motherboard thing and I still don't get why this is such a good measure considering the CPU already costs more and RAM is now apparently equal in price to motherboards (both of which would fit into the electronic circuit boards kWh/kg metric but require far more energy by weight). Those boards are also all mini/micro ATX and I've been talking this whole time about normal form-factor boards. Look at a 500g CPU/RAM/Motherboard combo at 3300 kWh/kg and I still don't see what the problem is. The real problem is we're operating in the dark making fighting on this number pretty pointless.

Fighting for a cent / kWh at this point when we just don't know represents a 20% change each time in the calculation. No global-scale motherboard manufacturer operates in Beijing - that would be like setting up shop in their version of NYC. Look at Foxconn - they go to where the power and labour is cheapest. To the point where they've developed a pretty bad reputation for their treatment of employees.

And telling me that my post is finally "in the realm of possibility at least" is kinda condescending. Truth of the matter is I have a desktop that's on 24/7 and consumes just shy of 350W according to my Kill-A-Watt (350/4 base + 1230 running kg CO2eq / year). My 3D printer gets used maybe once a week for a couple hours (100/4 base + 22 running kg CO2eq / year) making its carbon footprint only 3.5% that of my desktop per year. I did a lot to try and get to your way of thinking including double numbers for no reason and picking the highest of each estimate but this reality has always been sitting in the back of my mind.

My desktop is at least an order of magnitude worse for the environment than my 3D printer. Even if I printed for an hour a day, my 3D printer only reaches 7.8% of the CO2 footprint of my desktop.