Msi p7n sli-fi lga775 (cpu)

Ok. My name is Rob and I am most definitely a noob at this. My problem is I do not know a ton about CPU's, only what I read and understood with some research. My hope is that with the information I can provide someone can help me pick the best CPU for my machine based on spec's and price.

I have:

* 9800 GT Graphics Card
* Creative Sound Blaster X-Fi Sound Card
*NVIDIA Barebone:
* MSI P7N SLI LGA775 ATX Motherboard
* Cooler Master NV-334-KWN1-GP Elite 334 nVidia case
* 650 Watt Power Supply

* I am Running XP
* I currently have 2 GB of RAM but plan on upgrading to 4 GB ( and maybe eventually 8GB)
* 1 TB HD
* LG - 32" Class / 1080p / 60Hz / LCD HDTV

So Some of the CPU's I was looking at were:
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Intel Core 2 Quad Q9550 Processor- 2.83GHz, 12MB Cache, 1333MHz FSB, Yorkfield, Quad-Core, Retail, Socket 775, Processor with Fan


Intel Core 2 Quad Q9505 Processor - 2.83GHz, 6MB Cache, 1333MHz FSB, Yorkfield, Quad-Core, Retail, Socket 775, Processor with Fan


Intel Core 2 Duo E7600 Processor - 3.06GHz, 3MB Cache, 1066MHz FSB, Wolfdale-3M, Dual-Core, Retail, Socket 775

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I am not stuck on any one of those, they were just some I was looking at. SO if you have any suggestions I would really appreciate them.

Thanks a lot

Rob