As far as "3D MARK" increases go, you'll only benefit in the cpu tests with a quad-core.......your SM 2.0 and 3.0 scores will not increase.
You can easily do other things whilst gaming as a result of having a quad (encoding movies, folding, etc etc) which would normally be impossible on a dual-core setup due to having two less cores. People seem to view a quad in the sense that it somehow enables your gpu to churn out more FPS (or atleast it should), and when it doesn't they yell "Quad-core is overkill, no games will use it." Which would be relevant if only pc's ran a single app and that app were a game. Windows is multi-threaded and if you have 7 applications open on your pc then windows will multi-thread them all, by which I mean while each application itself may not be multi-threaded, windows will send threads from each seperate application to different cores thus spreading the workload and enabling greater performance/smoother execution of those applications/games compared to a dual-core setup.
Basically if all you do is play games, or if when you play games you NEVER run any apps in the background then you'll be fine with a dual-core. If like me you fold for rosetta, encode movies quite a bit etc etc.......and wish to run these applications whilst gaming and maintain the same gaming performance as you would on a dual-core setup then a quad is for you
