well you have a choice of what multiplier to use with your memory,
if you run 200x20 on the processor, you could run x6,x8,x10 on the memory to have 1200(200x6), 1600(200x8) or 2000(200x10) MHz memory speeds. 
I run 200x20 for daily use, and since my memory is some cheap DDR3 1600 at 9-9-9-24...