its good to go with an X2, but if you are going for extreme/hardcore gaming, then its best to get the 6000+. But its better to get a Quad now to future proof your rig. The Phenom performs better than the X2 from what i have seen
So if you want a good CPU for a long run, then get a Quad, if you dont mind switching maybe in a few months, then get an Dual.
Look at this
Even though the quads clock is lower than the dual, it still performs better. Not by much, but in a few months, then the difference will expand. But it seems that the Phenom is doing good compared to the dual core 6400+.
But a CPU will only be good for gaming if you also have a good enough graphics card.