SiSoft Sandra Mandelbrot
Next up is SiSoft's Sandra system diagnosis program, which includes a number of different benchmarks. The one of interest to us is the "multimedia" benchmark, intended to show off the benefits of "multimedia" extensions like MMX, SSE, and SSE2. According to SiSoft's FAQ, the benchmark actually does a fractal computation:

This benchmark generates a picture (640x480) of the well-known Mandelbrot fractal, using 255 iterations for each data pixel, in 32 colours. It is a real-life benchmark rather than a synthetic benchmark, designed to show the improvements MMX/Enhanced, 3DNow!/Enhanced, SSE(2) bring to such an algorithm.

The benchmark is multi-threaded for up to 64 CPUs maximum on SMP systems. This works by interlacing, i.e. each thread computes the next column not being worked on by other threads. Sandra creates as many threads as there are CPUs in the system and assignes [sic] each thread to a different CPU.

We're using the 64-bit version of Sandra. The "Integer x16" version of this test uses integer numbers to simulate floating-point math. The floating-point version of the benchmark takes advantage of SSE2 to process up to eight Mandelbrot iterations in parallel.

The dual FX-74s are more than twice as fast as the Athlon 64 FX-62, but the Core microarchitecture's ability to execute a 128-bit SSE instruction in a single clock cycle gives it an insurmountable advantage.

Windows Media Encoder x64 Edition
I had hoped to use QuickTime Pro to do some high-definition H.264 encoding, but QuickTime apparently maxes out at two threads. Windows Media Encoder works fine with four threads, though, and comes in a 64-bit version. For this test, I asked Windows Media Encoder to transcode a 153MB 1080-line widescreen video into a 720-line WMV using its built-in DVD/Hardware profile.

This is another close one, but the QX6700 take the top spot. Multi-core processors do offer speed gains in video encoding, but as is the case here, those gains don't tend to be linear like they can be in 3D rendering.