1 Quad-core Vs 2 Quad-core, performance comparison. Options

[alainmallet]

Been using a G5 dual 2.5 for a few years now and I'm about to embark on a big solo project so I want to switch to one of the newest Mac. Given the price and the fact that I'm going to have to buy some new software and PCI cards as well I'm trying to make the most educated decision. The first step is to decide between 1 quad core or 2 quad core system. It seems that bigger isn't always better in this case and the reports can be a bit confusing so I'm turning to the Mac community for help. I use Digital Performer as my main sequencer and Reason 4 as my main sound source. I also use the UAudio sound cards and run most of the usual softwares within DP ( all the Spectrasonics stuff and many NI softs)
Is there a clear advantage to getting the 2 quad core Mac over the single quad core. If you are using similar softwares feel free to suggest some favorite configurations as well.
Thanks