If it's only gaming then save the $$ from the dual core and be sure to get at least a 7800GT based video card.
But if you do more then gaming on it ... Publishing, Web design, Programing, Video Editing ... then the Dual Core is definetly the way to go. Once you go Dual CPU for "work", you never want to go back. I use my Dual Xeons at home and at work they got me a nice Pentium D workstation. The other boxes below are almost excusivly gaming.