Actually we DO know that the SLCD3 is more energy efficient: this display uses the SHARP IGZO (indium gallium zinc oxide) process. Sharp has said that products using this display technology last 2.5 times longer overall in battery life than products without that display. That said, the Adreno 320 in the APQ8064 is a beast of a graphics processor: we are seeing this in the LG Optimus G and Asus Padfone 2 without the benefit of Jelly Bean (they both run Ice Cream Sandwich) and both of those devies are benchmark monsters.
HTC is well aware of the battery criticism they've had for their large screened, 4G devices, hopefully they've done the math and found 2,020 mAh sufficient for this LTE device.
And yes, the Japanese version is IPX5 water resistent. Here are the specs straight from the horse's mouth:
HTC J butterfly HTL21 - HTC Smartphones Here's hoping we DO see the HTC6435LVW as the Nexus 5 this year, but it could end up being December/January in anniversary of the original Nexus One.