My first advice to you [Edit: as I now see JR suggested already] is to fill in all your system details as much as possible in your CP (control panel) [use the link I provided to try to figure out which memory-modules you have] so we all can see your specs try to fill in as much as possible (if ya dont know we might be able to help you regardless.
but for now you should leave the mems @ 1.65v like suggested by MRCL, until you/we know EXACTLY which RAM-module/s (DIMMs) you have.
And when you know the Part No: like "KHX1600C9D3X2K2/4GX" then u can download the datasheet (probably in a pdf-file) however someone here can also DL the sheet here:
http://www.kingston.com/hyperx/products/khx_ddr3.asp
We can not help you (without taking a wild shot in the dark) until we have this input as different DIMMs are specced for lower/higher voltages and have lower/higher latencies, & the difference between single/dual/triple-channel kits + if you have fully occupied all of your RAM-sockets on your moteherboard.
There is a bunch of stuff to learn about mems (SDRAM/DDR2/DDR3), but here on TPU u can be sure to get the help you need even if it may take time + some effort from your side too.
Finally you will be able to ramp up the OC & Voltage/Timings @ exactly the setting you prefer barring the "too much OC" & the DIMMs can´t handle more voltage even if you loosen your timings on the DIMMs (like a heat wall) but hey place a fan blowing on them heatspreaders on the mem/s.
EDIT: you may be able to OC the mem/s without raising the voltage [but i doubt your system will be stable 24/7], I reached about 90ish MHZ OC @ 1.65v with mine but they weren´t stable, so I settled for 66MHz & tighteninged the timings a bit. (however mine were set @ 1,5v in BIOS as AUTO but the box were printed with 1.65v)
I talk too much every now & then so enough spoken for now.
Laterz
//Dog