OCWorkbench have got an exclusive review of the ECS P4S5A SiS645 DDR Mainboard. Heres a clip:

    As the first S478 board that officially supports DDR333, it is very appealing compared to the P4X266 which only officially supports DDR266 and newer revisions of P4X333 will support DDR333. Performance is excellent in content creation and 3D. In fact, the P4S5A scores comes real close to the RAMBUS solutions.