That RAM will run at DDR533 as a default anyways. If you were to try and use that RAM and keep your current divider, you will be running your CPU at 4.8GHz, which is practically unachievable.
You can reduce your multi down to 4 to keep your CPU running at the same speed. However, this will not really give you a huge improvement in performance.
And then I just noticed that you said you are not going to be overclocking. Then it is definitely not worth the extra money to get the faster RAM.
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