I watched a side by side comparison the other day on YouTube between the international and U.S version of the Samsung Galaxy SIII. The international version is a Quad core and the U.S. version uses the Dual core. Side by side, really about the only difference was the Quad core booted up about 1-2 seconds faster. Games loaded faster about 50% of the time. The tester ran the test using identical setup phones in a clean room using the companies WiFi connection.
I think the Dual vs Quad debate comes down to the effectiveness of the OS to run with it more so than the actual speed of the CPU be it iOS, WP, Droid, BB, Symbain, etc. The OS has to be able to use the CPU or it's just wasted battery life.