The numbers for the MPEG4 encoding task look more true-to-life. At least, the CPU frequency is the decisive factor here to determine the overall system performance. Note also that the platforms with Pentium 4 2.4C overclocked to 3GHz and DDR500 memory are running faster than their analogs that use DDR400 with the diminishing coefficient, notwithstanding the more aggressive timings in the latter case.
It is the CPU speed that determines the system performance during final rendering (ray tracing and shadowing) in professional packages like CINEMA 4.0. That is why we see nothing extraordinary here.
The nature of lighting algorithms is different and the memory speed is the most important thing for them. Thus, Pentium 4 2.4C overclocked to 3GHz and using DDR500 in the synchronous mode manages to outperform itself, overclocked to 3.3GHz and using asynchronously working memory.