minimal possible voltage you have to find it yourself. Mine is 1.36.
Try to let everything on auto except for vcore at 1.38 lets say.
raise the blck to 200 and set 20x your ratio.
Althought your ram is not the best for overclocking :-/
Did you mean for OCing the CPU or the RAM itself? Because 99% of the time you won't notice a difference when OCing your RAM (and if you're not really familiar with it, RAM OCing can be frustrating and even take speeds down sometimes depending on the intervals in relation to your CPU).
But yeah, like abs said, you have to just find it yourself. Mine is at 1.384 (or something near there) and I'm running at 3.8GHz with a peak temp of ~50c (i5 as well).
Good luck with it and keep up posted!