I'm planning to buy Quad Core to replace my Core 2 Duo E6420.. I have Sapphire HD5450 1GB DDR3. If I upgrade my CPU to Quad Core, will it improve my graphics performance? Also, what are the benefits of a Quad Core?
Sometimes
You can multitask single and dual threaded applications faster, and you can run quad threaded applications with much more efficiency.
Yes
Some games show absolutely no performance gain from dual to quad - even some 2010 and 2011 games. But recently, more games have been showing a modest to significant increase. A couple are even to the point where a dual core barely passes, while a quad does just fine. It depends on the game.