Unless you're going to wait for Bulldozer, the only significant upgrade from the Phenom II X6 right now is Sandy Bridge. The i7 series may be dual-threaded quad cores, but the architecture is still superior to that used by the Phenom series. I suspect Bulldozer will basically get the same performance as the 2600 with the FX versions having unlocked multipliers like the 2600k at the same ~$300 range.
