I have a LG LX9500 3D capable tv, and am currently using an HDMI version 1.3 cable for my PC and videogame console.
I'm wondering if upgrading to an HDMI version 1.4 cable would have an effect when viewing 2D content; like smoother playback, less lag etc.
No such thing as an HDMI 1.3 or 1.4 cable. 1.4 refers to the HDMI hardware spec, not the cable spec. All you need is a Certified High Speed HDMI cable from a reputable mfr such as Monoprice, MediaBridge, BlueJeans, etc. The cable should be certified for the length that you purchase. You don't need to spend a ton of money on the overpriced HDMI cables such as the "M" brand or others that you'll find at BB, etc.