How can that be answered? One is a dual core, the other a quad core, they are entirely different CPUs. You haven't specified which i3, which phenom, or what programs you'll be using. For games, any i3 will beat almost any Phenom II X4, but if you're comparing the i3 530 to the X4 965 Black Edition, then it's going to be reasonably close on some occasions. In multi-threaded software, the Phenom II X4 will win because it's a quad core, but if you want a quad, buy a Core i5 750 instead, much better.
