Your ram is currently not at 1:1 ratio. Basically if you run a 1:1 ratio, then that means your RAM is running at the speed of your bus speed. So for your current setup QDR 1333mhz, your bus speed is 333mhz. That means your memory would be 667mhz or 333mhz *2.
However because you have an Nvidia 750i chipset, you can easily run the memory unlinked, at 800mhz all the time.