MY XPS 600 RAM

​ I swear when I bought my XPS 600, I ordered it with the new 667mhz Ram. I purchased 1 GB, opting to upgrade myself down the road. ​

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​ I have no arrived at the end of the road. I have an XPS G2 Desktop, and I added Corsair XMS Extreme Memory that was 400mhz (fastest at the time) and I have been very very happy with Corsair. ​

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​ I'm looking at the new Corsair, and they have PC5200, PC5300, PC5400. Which do I chose? ​

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​ I tried using CPU-Z and Everest Home, but neither will tell me the Mhz of my existing 1 GB. ​

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​ Thanks in advance to all who can help. ​