In preparing a print article today, I went back to check my April 2010 research and to my chagrin, could not find it. I discovered that a page I had written just never had gotten linked into my review of the Mac Pro, but it is now in place.
Shouldn’t twice the memory and twice the cores be at least a little faster? Nope. And it’s why I advise most MPG Pro Workstation customers to go with the 3.33GHz 6-core.
Rest assured that 12 CPU cores can be better than six for a few specialized tasks, but not very many, and the software makes the difference. See all the tests for specifics.
Read the details in When More Is Less: Photoshop Slower With 12 Cores Than 6. I’ve reconfirmed that the issue still exists as of today with Mac OS X 10.6.6 and the latest Photoshop CS5, 9 months after I reported it to Adobe back in April 2010.