If I get the 40 kWh battery, will it be able to charge at the same rate as the 85 kWh battery? -- assuming same charging equipment and same outlet.
You will be able to charge at the same rates as the other batteries. You will not be able to use a 'Supercharger' which is a 90kW high voltage DC charging station. At home, at a RV park, at work, at any AC charging station you can charge the same rate as the other packs.
10kW with 1 charger ~ 32 mi / hr charge at max or 2okW with the 2 chargers ~ 62 mi/hr which seems unnecessary for a 4okWhr battery especially if it is a city car
Something about this post made me realize that a base Model S could be fully charged off AC in about 3-4 hours. That seems quite reasonable. For some reason putting it this way just sounds better to me .....