Answer: you can't, go learn about computers.
I know that's a bad answer, but that's the right one (in a way).
It depends heavily on what you use the computer for, of course. If you just run games, the RDRAM would be faster. If you run Photoshop, Bryce, 3D Studio Max, Maya, GoLive, Word, Excel, Powerpoint, Access and Outlook all at once, then you'd probably need the extra RAM.
<font color=blue>Quarter pounder inside</font color=blue>
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