In gaming, the x6 will function as an actual 6 core. The Fx 6xxx series will perform the same as a tri-core in games, due to the shared FPU units (One FX module shares an FPU unit between two cores).
However, the x6 is overpriced. It's essentially a x4 with two more cores; I don't think that the price tag justifies that purchase.
The good thing about the FX series is that they're quite a bit easier to OC than the Phenom series.