It was mentioned on other posts, but the MB clock is actualy 1/4 of the CPU's FSB and the DDR2 clock is 2*MB clock (if set to 1:1 ratio). So on your 1333MHz advertised MB, the board's base clock is actually 333 MHz and if you set the FSB to RAM ratio to 1:1, the RAM would run at 666MHz.
This would also mean that with DDR2-800, you could potentially reach a FSB of 1600MHz (and many people do with Q6600 and E8400 CPUs).