Overclock is the easiest way to improve performance on Samsung Galaxy S III. Samsung Galaxy S3 Quad Core Application Processor is clocked at 1.4 GHz by default. However, you still can push its limit and improve overall Samsung Galaxy S3 performance by overclock up to 1.8 GHz. Official Samsung Galaxy S3 kernel does not support overclock feature. So you need to install custom kernel for Samsung Galaxy S3 in order to overclock.
Note – overclock will reduce Samsung Galaxy S3 Quad Core Application Processor and other hardware components lifespan because it will overheat easily. Do it at your own risk.