When you think about how big 82" is that is a fantastic price. There are a few additional upgrades that the 840 has:
Bluetooth audio streaming
ISF adjustments
Additional picture controls
Wired IR input (for RF remote control)
Additional HDMI (4 total)
Clear Contrast Screen
I's be curious about the screen upgrade. I don't know if its an actual upgrade or marketing BS. I'd ask your friends if its worth the $200 upgrade or not.