antiscab wrote: 112.5% more battery => 88% more range
the 85kwh option has more power, which may increase energy usage if driven harder
Also, the 85kWh version presumably has a fair bit more weight to lug around, even when the trips are small and the 40 kWh or even a 20 kWh pack would have been sufficient.
It's almost like the hybrid verses pure electric argument. With the hybrid, pure electric advocates point to the waste of carrying around a ~~ 200 kg engine that might rarely be used. With the monster pack in the Tesla, the last 45 kWh of energy, which might weigh ~~ 300 kg, could be considered a waste, since the last 45 kWh might rarely be used.
It depends on the usage pattern as to which pack will work out best for a particular vehicle owner. Ironically, with an ICE, a large fuel tank costs only space, and a little weight for the extra tank size and chassis to hold it. You don't have to fill the tank with fuel if you know you won't need it. (Not that an extra 50 litres of petrol or diesel weighs all that much - perhaps 40 kg). With the monster pack Tesla, you don't have to charge it full, but it will still weigh the same fully charged as when is only "half full".
[ Edit: the last post on this page: acceleration and weight (Tesla Motors Club) suggests at least a 140 kg difference between the smallest and largest packs. Actual pack weights seem to be guesses at this stage. The Model S seems to be gambling on an advanced chemistry. ]