Faster RAM is just for if you overclock. No board officially supports anything over PC3200. Dual channel is just combining two seperate memory channels together to get (theoretically) double the performance). In the case of the Athlon 64 as an example, you've got three processors with pretty similar performance:
3400+ 2.2GHz, 1MB L2 Cache, single memory controller (socket 754)
3400+ 2.4GHz, 512KB L2 Cache, single memory controller (socket 754)
3500+ 2.2Ghz 512KB L2 Cache, dual memory controller (socket 939)
All three have pretty similar performance, and no one is absolutly superior to another. It's kind of a good example as to how dual channel combines with the amount of L2 cache and the clock speed to get similar levels of performance.