Is this board going to be free? I really don't understand why you would want two of the same boards in different sizes... actually, I can see why. The 161.5 Rice is pretty much a different board without the blunted tips and wider waist.
I say go for 161.5. Do you find the 157 to be stiff? Keep that in mind before you consider the 164 because it's going to be even stiffer.