i'm planing to upgrade my ram to 2gb/4gb, but still confusing either go for DDR2 800MHz or DDR2 667MHz.

here's my pc spec:
Gigabyte GA-P31-S3L, FSB 1333MHz (4 x 333MHz)
Intel Core 2 Duo E6550, 2333 MHz (7 x 333MHz)
RAM - 2 x 512MB DDR2 667MHz (333MHz x 2) dual channel

since my bus clock is running at 333MHz, if i swicth to DDR2 800MHz, then my clock speed will be 400MHz izit?

should i go for 800MHz or 667MHz?