The more multi-processing you need, the bigger the 8-core advantage over the 6-core.
A friend decided on an octa for his studio, but he's on Logic and Nuendo, with lots of plug-ins and high track counts. The eight-core is definitely the better option, there, as those applications are heavily optimized for parallelization.
Edit: Wait, I'm confused. There is no "new" 2.24 GHz octacore machine. Watcha got, dkrz?