1) There are no good dual core AMD CPUs. Well, they aren't bad, but they do not compare well at all with Intel. The newest AMD quad cores ALMOST compete with Intel, so they are a better choice. Because AMD dual cores are slow, they tend to bottleneck GPUs more... but a really fast one is enough if we are just talking about one 4850.
2) Crossfire is for running two ATI video cards. You do not need it to run one.
Get the best of both worlds with the Q6600. It is close to the same price as the E8500 and can be OC'd to 3.0-3.2. Maybe higher but you can get those speeds with some of the auto settings.
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