The weight should be about the same. Elon stated that the increased capacity is a result of a change in the battery chemistry; they added some silicon to the anode. Unless you're talking about a minor change on the atomic level, there won't be much difference in weight. The battery is only 24-25% of the mass of the Model S, and a tiny change in that shouldn't be enough to affect the 0-60 acceleration time.
Yea, but he also said that the range and ludicrous upgrades are "almost" entirely independent. If both packs are limited to 1500 amps by the new e-fuse, it's possible the new pack could put out more wattage if the voltage curve has shifted to the right under the same loads.