I went for the older '08 2.8 ghz model. With the money I saved, I put in 4x 1tb hds, and 16gb of ram.
I make music (yes, the ram is future-proofing, but certainly not needed now!) and this thing is amazing. ALL music programs are compatible with it RIGHT now (protools, ableton, logic pro, UAD2 which i ALL use...)
Basically, I can't tell you how good it feels to load up a complex project, even w/ omnisphere, and see ALL 8 cores happily running @ 25-35%. This thing is a dream, and I can honestly say there's no way I need anything more than this.
For audio, 8-cores is a must, it can handle anything you throw at it! I would never choose a 4 core over this thing!