Well, the thing is, I already have the ram, it's in my sig. Defualt is 1600MHz@cas9, but I can down it to 1333@cas7, 1600@cas9(Defualt), or 1866@cas10. Out of the three choices here, which would give me better performance, regardless on how much boost I get.
They would pretty much counter-balance each other. Raising the mhz (good) also means raising the cas latency (bad). There would be so very little real world difference, I don't think you should even worry about it.