i made a more dramatic jump (from a quad G5 2.5 to an OCTO intel 2.8) back in january. and was surprised that there wasnt as much improvement in times as id have hoped. significant improvement was made - just not as night and day as i would have imagined...
what gave the most performance increase was adding 16 gigs of ram and moving my scratch disc from a firewire800 drive to an eSATA situation.
here are 2 threads that elaborate:
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www.lafcpug.org]
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www.lafcpug.org]