I think the original goal was a world record production car in terms of acceleration. Which means beating not only the 911 Turbo S, but also Veyron. That's why I erred on the side of caution when considering target numbers. And I'm not making any assumptions about how the power to weight ratio scales or how much less max power an EV can make do with. I just picked slightly better numbers than cars that have shown they are able to get sub 3 second 0-60.
As for a multi-speed transmission, I also find it unlikely Tesla will bother. 0-60 is something you can experience even on public roads; top speed isn't. Plus only a small percentage of sports cars/super car buyers actually drive on the track (some super cars are barely even driven in the first place!). Seems like a lot of engineering (and possible loss of efficiency) for something that will rarely be used.
It's actually possible to have both 0-60 and top speed given lots of power and with very high gearing (direct drive or close), examples:
I just noticed the Eliica (which has both acceleration and top speed of 200+mph; its almost a electric Veyron) "only" has 480kW of power and weighs 2400kg/5300lbs. I think a Model R with 440kW and around 3500lbs should also have pretty amazing performance.