Hi mikk1234,
The difference is util if you overcloking the CPU and (or) the Ram,
Because when you oc, you adjust a tensions and volts.
So if the Ram have a possibility to up 1.65, this is the best.
But in normal situation, 24h 7day, the Ram is ajusted to 1.5 volts, sometimes 1.45, 1.40 volts. Especially with Sandy Bridge CPU.
We must not forget that Sandy Bridge CPU has one memory controller.
In normal time, the objectives are to have less tension and therefore less the heat to be dissipated by the memory.
When you overclock the ram, there is more heat and of course, we must not damaged the memory.
Glouup_Gloup