Is that a 6-core vs a 2-core? More cores, for sure, if you're doing rendering. And most people seem to dislike ATI over NVidia, something to think about.

I have an i7 920 which I really like, with DDR3 RAM.

What's your budget is the first question.

Oh, and if you can spare the cash, I really like having an SSD for OS and apps, and a big HDD for data.