On that board no, AMD allows a much wider range of memory multipliers relative to the system bus than Intel does, and that board has a drop down menu of speed options, select the right one and it will set the appropriate ratio and multiplier for you.
For OCing a 1090T, first, you will never get your base clock up to 800MHz on an AMD system, second, the 1090T has an unlocked multiplier so you just set that to 20 and its at 4GHz, you will likely need to tweak the voltage to get it stable but since you would be adjusting the CPU multiplier you wouldnt even need to touch the memory setting again.