Sandra
Sandra is still a very useful memory benchmark, and the Crucial Ballistix PC2-6400 does quite well here - it is only 2.4% slower than the Corsair XMS2 PC2-8000. Please note that in both cases, the top results are more dependant on having the fastest FSB possible than the fastest DDR2 speed; however high speed DDR2 sticks leave us with more headroom for faster upcoming FSB's :-)
WinRAR
WinRAR is a great benchmarking tool as it is affected not only by memory, FSB and processor speed, but also by memory latency. Here we see that the lower latency PC2-5400 stick (at 3-2-2-7) beats the higher latency PC2-6400 stick (with 4-4-4-10 timing) - but both are beaten by the PC2-8000 sticks.