I sometimes render out videos but it would mainly be used for gaming
6 or 8 cores can come in handy if you are encoding video and if the codec you use can make use of multiple cores. For example, the x.264 codec can take advantage of 8 core (if I am not mistaken), however, if you encode videos using the older XviD codec then 6 or 8 cores are overkill since XviD can only use one core (despite claims of being multi-threaded).
The vast majority of games only use 2 core. Games capable of using more than 2 cores represents a small fraction of games released every year. BF3 is one of the very few games that can make use of more than just 2 cores; but only in MMO mode.