x11's are great, because they are hardwired, cannot die, and have amazing sound AND can be used with a computer. x31's however, have better sound and three different sound modes that can pick up different types of sounds better, i actually own both sets. the x31's are wireless and all around the sexiest headset ever, the downside to them is that they eat batteries like a fat man eating chinese food.
they're both are heaps better then the wireless/standard headset for xbox which are fine for casual gamers, but if your on MPGH, you're not a casual gamer.