All the SB overclocking guides I have seen say not to worry about the Ram.
If it is 1.5v, 1.65 etc. dont worry just set it to its correct voltage.
This is what was posted on a very good guide by Clunk.
Sandy Bridge has only been around for a short time, but sadly, there is an incredible amount of confusion regarding certain aspects of voltage adjustment. The information below, comes directly from Asus, Gigabyte, Corsair and Intel PMO (Platform Memory Operations), and to the best of my knowledge is 100% correct at the time of writing this. Of course, if any new information comes to light, I will update this section.
* Sandy Bridge does not demand only 1.5v modules, it will be perfectly happy with 1.65v modules too. If someone tries to tell you that you must have 1.5v modules, then they are either trying to sell them to you, or they have been reading misinformation, or both! Another point to consider here, is that in your BIOS, if you head to the memory voltage setting, and enter 1.5v, the text will remain white/grey, if you enter 1.65v, it will turn yellow, and it isn't until 1.73v that it turns red, so at the moment, I'd rest assured that 1.65v modules are OK to use, and I have had this confirmed by Asus, Gigabyte and Corsair so far, as soon as I hear from anyone else, I will update this again.
Here is the full guide!
http://www.clunk.org.uk/forums/overclocking/39184-p67-sandy-bridge-overclocking-guide-beginners.html