In large System-on-Chip (SoC) architectures, balancing the clock network is increasingly difficult. Globally Asynchronous Locally Synchronous (GALS) removes the need for global clock net, and also provides efficient means for managing the complexity and re-use in large architectures. However, quantitative comparisons of GALS against similar synchronous structures are rare for full SoC architectures. In this paper, we compare our SoC GALS architectures to a synchronous architecture with a fully functional MPEG-4 video encoder on FPGA. The results show that the area and performance overhead of GALS is only 1%. That is negligible compared to the benefits of the GALS architecture such as multiple clock frequencies for Intellectual Property (IP) blocks and dynamic frequency/voltage scaling, clock tree removal, and re-usability. Our architecture does not require modifications to the IP blocks already used with synchronous architectures, providing an ideal solution for rapid switch to GALS architecture.