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Memory - Intel recommend 1.50v plus/minus 5% which means 1.60v is the ideal safe maximum, but we have found in our testing all 1.65v memory is fine. We have also found most new 1.65v like Corsair XMS3 will run at its rated timings with just 1.50-1.55v which is well within Intel specifications. So people upgrading to Sandybridge you can still use your old DDR3, but we do recommend you run it at 1.60v or less. We are shipping most of our bundles which feature Corsair XMS at 1.50v-1.55v at rated timings. We've also discussed with Asus and MSI regarding voltages for memory and they also confirm in their testing 1.65v caused no issues with reliability
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Sandybridge maximum safe voltages
Core Voltage - Not recommended too exceed 1.38v, doing so could kill the CPU, we therefor recommend a range of 1.325-1.350v if overclocking.
Memory Voltage - Intel recommend 1.50v plus/minus 5% which means upto 1.58v is the safe recommended limit. In our testing we have found 1.65v has caused no issues.
BCLK Base Clock - This is strictly a NO, anyone using base clock overclocking could/will cause damange to CPU/Mainboard. (Set manually to 100)
PLL Voltage - Do not exceed 1.9v!!
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About 4th post down.
http://arstechnica.com/civis/viewtopic.php?p=21199063
!.5 V is better - that said. I have DDR3-1600 ripjaw CL7 @1.60 Volts in both my I5-750 and My New SB build.
In reference to speed and Cl timings. generally less than 5% boost in performance going from 1333 -> 1600, and also generally less than 5% for CL9 -> CL7. There are a very few apps that can take advantage of inceased BW (Speed) and lower timings.
That said, again my preference is for DDR1600. NOT if the memory is rated @ 1.5 V, but not totally stable you could always increase VDimm to 1.55V, BUT you should not do that with 1.65 V rated Ram.
PS. Intel plays it a little conservative with Voltage. I try to stay under the 1.65, but feel safe with 1.60. Higher speed ram (1600 and Higher) has only recently dropped below 1.65. The vast majority above the 1600 is still @ 1.65