Need help with Ocing Ram/voltage

hi all and thanks for any replys in advance basically i have my kingston 2x2gb khx1600c9ad3b1/2g ram at stock 1600mhz ive already Oced my Cpu to 4.7Ghz im using intel p8p67 deluxe MB on the ram it states 1.65v but yet i check online and it says voltage is 1.5 for these memory sticks khx1600c9ad3b1/2g.

so im guessing but not sure i can go to 1.65 volts for overclocking to say 1866/2133 but is this ok to do without any mini Ram cooling fans above them how far can u go on non cooled Ram