I7 K series Quad Core or Amd II X6?

My current system is the one in the sig but my dad would like to buy it for his office for $700, but I keep the 1TB Caviar Black and the GTX 260. I would have altogether to spend towards the new rig about $1200. I'd use the 1TB HDD since it has all my movies and videos. So for my new rig, I was wanting a Sandy Bridge i7 2600K or a 875K and overclock it to 4GHz. Or get a X6 the 1055t or 1075t and overclock that to a 3.4-.6? Which would be better? I do light gaming, not a hard-core gamer. I usally watch a lot of movies and stuff. My Overall CPU usage on my current i7 is 5% at idle and 30% under MY Max Load which is Blur the game. I have not idea if 6 cores or 4 cores. I want to be future-proof and a 6-core 980x, is something I can't afford. Should I just stick with a 4 core i7? If so, a 875K or wait for Sandy Bridge? Thanks for any replies and suggestions!