Even @ stock voltage it can achieve 4.2Ghz with rock solid stability. This chip, is made to over-clock
With the 6 cores it'll fly through anything you throw at it and will breath fire if you tell it to.
Video editing/encoding is a breeze, gaming a pleasure. Everything you throw at it is spanked as fast as greased lightening.
It isn't cheap, but it's very slowly coming down in price and there are a few available second hand as people switch to the 2011 platform. The 990x will give any 2011 CPU a run for its money and still beat them over many applications.
If you want THE best CPU there is for the 1366 platform and the freedom of an unlocked chip to over-clock in excess of 5Ghz + go for a 990x , it is the business, you really won't regret it.
If your upgrading your existing socket 1366, you'll have a dilemma......
Do you spend loads of cash upgrading your 1366 board and memory and still have to buy a CPU to go to socket 2011, or buy a 990x that will slot straight into your existing kit and have as fast as PC as any 2011 setup and that's good for another 3 or 4 years.
Its a no brainer really, get yourself a 990x and extend the life of what you've got. Trust me, when you get one, you'll see why they have held their price.