Do you still have a 9600BE?

C3 DDR2-610 = 5ns
C4 DDR2-800 = 5ns
C5 DDR2-1000 = 5ns
C6 DDR2-1200 = 5ns

C3 DDR2-692 = 4.34ns
C4 DDR2-692 = 5.78ns

C4 800 is not much better than C4 692, although it would make a difference, but only in very memory intensive benches (like 32M).