You know you could always get an e8500 it would save you 80 and you easily just overclock for less and it would offsett some of the cost of the Mushkin ram. You might look at the motherboard/cpu combo that newegg has you could save more money there too.
Going from a 9600GT to a 4870 yeah you'll see an improvement and if its not enough save you're pennies for an awesome crossfire rig

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