DDR400 has the same clock rate as DDR2-400 and performs better.
Yes, both the 800 bus and DDR400 are based on 200MHz clock cycles, these run synchronously together.
But these days the performance difference of running asynchronous memory is not that noticeable.
Maybe for newer pc's you don't notice a difference. On my current machine, I ran Sandra tests before, during, and after putting up my fsb. Then i ran a tests just to see if 1:1 ratio works or not. With my ram being 1:1 with my fsb I run averagely about 9% better.