Cool, some numbers. First off, looking over your math, it looks correct, so that's good. The article seems to be a bit confusing, however, or you're taking a best case scenario they don't approach in the article. It states that an EV takes 8.8 tons of co2 to produce. It later states, however, "However, a BEV (battery electric vehicle) produces less harmful emissions over its entire life. The study found that a medium-sized petrol or diesel car produces around 24 tonnes of CO2 versus a BEV’s 18 tonnes" this seems to imply to me that we shouldn't keep emissions at 0 throughout the EV's lifetime? I would assume this additional tonnage is from less-clean electrical generation methods and overall maintenance requirements.

If this is the case, it paints a bit different of a picture, more in line with what I said - that you should buy one if you're going to buy a car anyway, and drive yours. What the numbers provided does give us now, though, is a point at which the sunk cost DOES become too large, and that seems to be a car in the age range of 10-15 years at present.

Please, if I've misunderstood something with the article, correct me, and thank you for the write up with sources.