IMHO if you are going to using game mode I would say the 8 over the 7, for me though it is because you can do a 1D LUT on the 8 series for the game mode where you are stuck with the available controls of the display itself to dial in game mode. So you can never really adjust the grayscale on the 7 series in game mode. This is only if you are going to get it calibrated. If you're not doesn't matter much unless you want dynamic tone mapping in game mode. If you want that then 8 series.
Price wise if you find a 7 super cheap get it. If that extra bit of functionality is worth teh cost increase over a 7 get an 8
Thanks man. I am looking at January and happy to buy it if I can get an 8 around 1400.