Yeah, no offense intended but you're doin' it wrong. Phenom II X6. And gaming rig probably should never be placed in the same sentence.
The reason for this is that programs have to be optimized for multiple cores, and games aren't.
A thread is a string of commands that a program runs. One CPU core can run one thread. Unfortunately, its not possible to split up one thread among multiple CPU cores, because these commands must be executed in order. Also unfortunately, coding certain programs (like games) to have multiple threads is quite difficult, and right now game developers don't do it. Games older than the Source engine all run a single thread for the most part. So on a 6-core one core will run at 100% while the others sit there at idle not helping. On newer games, you generally see two cores used. That's still only 2 out of 6 cores. A few use three, and a couple four, but so far none use 6 yet.
What all that means is that right now a quad-core that is faster at tasks with less threads (such as the Core i5-750) are going to give much better gaming performance, and save you some money because P55 motherboards are much cheaper than 890FX boards (that Crosshair is a waste of money, motherboards don't have any impact on performance).