I just played CODMW2 on the 55" C7000, I had it hooked up HDMI 1 labeled game, and game mode was turned on. I had previously played almost 9 days of accumulated Xbox live multiplayer, all done with a 52" A650 using a VGA cable.
First let me state that the 55 C7000 picture is brighter, clearer, with more vivid colors. I can see the outline of people, where as I could only see there muzzle flash on the A650, also the detail is better. As far as lag goes the A650 was fine the way it was, it was not even noticeable. The C7000 felt like it might have had a little bit more lag the way it was set up, but I am not sure that it wasn't just me, I have not played CODMW2 in almost 3 weeks. I might have just been adjusting to the bigger, brighter screen, because as I played more I started doing better, and I did not feel that lag was an issue at all by the end of my session (about an hour and a half).
But being a gamer, and competitor at heart I will be looking for any advantage available, so if any one has any suggestions such as labeling it PC, or using LED motion, let me know. I do not want to go back to the VGA adapter at this time I am happy with the look of HDMI with game mode on.
Also if any one can post there settings, because I have been just using the stock ones (standard) with minor tweaks, to the backlight and brightness (lowering both a couple points).