Rendering what exactly i.e. what footage with what effects using what drives? All those things make a difference.
I wouldn't put those kind of bucks down on that machine just now. Certainly not just to run FCP at 32 Bits and 4GB of RAM. You'll get a bit quicker render times from the processors, but nowhere near enough improvement to justify the price tag.
Here's one guy's comparison:
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arstechnica.com]