06-25-2012, 08:08 PM
It depends on how you will be using the machine. The 6 core processor will probably get more performance out of the box due to having a higher clock frequency per core but if you own and use heavy software, the 8 core machine will yield better results.
Adding more cores substantially helps out certain VERY intensive CPU tasks such as high def video encoding however, you need to know how to set up your software to use it. The vast majority of the software out there is designed to use only 2-4 cores out of the box but a few programs let you change how they handle the CPU tasks by using an apple utility called Qmaster. In Qmaster, you select the compatible program, and adjust the amount of "instances" (aka tasks) the program divides across your CPU. It takes some trial and error but a good rule of thumb is to go half of the amount of cores in your machine to yield the best performance out of that program. When finished, you save the profile and select that profile in the corrisponding app.
Both 6 and 8 core machines are not designed for everyday consumer use. They require a user who is first of all running the software that can actually take advantage of all of those cores, and second, a user who knows how to set it all up. If you're just going to browse the web and play games, you're wasting your money on cores that will never be put to use.
As of right now, the only apps that I know of that can take advantage of Qmaster are Apple Compressor and Autodesk Maya. Compressor is relatively inexpensive but has a very specific use. Maya is heavy commercial software for 3D computer graphics and animation. The special effects on the Lord of the Rings trilogy were done on Maya and it is a very expensive program. $3,500 per license last I checked.
Other apps might be able to take advantage of all of those cores (FCPX maybe?) without having to go through Qmaster but I don't know of any off the top of my head. You can bet that they will be heavy stuff though.