What mommaboard do you have? Some mommaboards don't like certain voltages. You can always like... use a multimeter to confirm it.
Also, in order to overclock your CPU over certain values, yes it needs a bit more juice. This means heat and sometimes, the heat oddly enough won't make the CPU freak out, but any increase in temps will make its way through the mommaboard to the RAM and RAM is very sensitive to heat. To check this out, take the CPU up just past the point it got unstable at and loosen up the RAM timings all the way while you are at it. If it doesn't freak out, then it's a RAM issue and NOT a CPU issue. Then you might wanna give the RAM another 1/10th of a volt to stabilize it as well. If that doesn't work, I'd get a fan on the RAM before upping the voltage anything more than 1/10th over stock or falling in love with keeping a certain timing at the clock speeds you want to be at.
Also, as a general rule, I always advise to find your best clock speeds and then back off 20% of the amount you overclocked for safety's sake. RAM, and to a lesser extent everything else silicon does something I call burn in over time. I've seen Dude after Dude go and leave it at the ever loving limit. Next month, he can't keep it there and backs off another 15% and ends up doing this until he's way behind where he would have been had he not gotten greedy in the first place and admit it, you be greedy just like me and everyone else, so I understand the temptation!