I finally had a chance to do some input lag testing (using a Macbook in mirror mode with an on-screen counter and a camera at 1/60) and found some results that'll be of interest to anyone gaming on this screen.
There are basically two response rates that you can hit, 116ms and 16ms. 16 is great for gaming and 116 has a really noticeable lag.
The biggest thing to note is that the input number does not appear to make a difference, but the input label does. So even though Input 4 is supposed to be a "PC" input, it operates the same as the other inputs.
However the labeling of the input on the input select screen makes a big difference. For any label other than PC, "Game" mode is the only picture setting that will let you hit 16ms. For inputs labelled "PC", you'll get 16ms all of the time, regardless of the Picture mode.
Here's the most surprising bit....on an input that isn't labeled "PC", you'll lose Local Dimming when in Game mode. The option will be greyed out and it will very clearly be disabled (hello flashlights). However, if you label that input as "PC", you'll have Local Dimming support even in game mode and still have a 16ms response rate.
So would there be any reason to not label any input you'll be gaming on as "PC"? Not that I can find. I have an Xbox 360 and PS3 on an HDMI switch on Input 2 and my PC on Input 4, and it seems to make sense to label both of those inputs as PC.
I can't explain why Local Dimming wouldn't be available in Game mode on an input labeled Game, but would be on an input labeled PC. But if you're gaming and want Local Dimming support, it seems like labeling your input as PC is the way to go.
HDMI Input 3:
Labeled as "Game" input or not labeled
Standard settings - 116ms
ISF Expert - 116ms
Game mode - 16ms
No local dimming available
HDMI Input 3:
Labeled as "PC" input
Standard settings - 16ms
Game settings - 16ms
ISF Expert - 16ms
Local dimming options available
HDMI Input 4:
Rinse and repeat, it behaves exactly the same as Input 3.