endeavour37a :
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There were some reports several years back about Sandybridge CPUs burning out when used with 1.65 volt memory. These were traced back to faulty manufacturing at Foxconn with some motherboards being recalled (not related to the sweeping Intel PCH recall). At least one Intel service representative claimed that any CPU failure encountered while running 1.65 volt memory with an XMP profile would be replaced under standard warranty as long as there were no burn marks on the package.
XMP profiles are tested and certified by Intel before the manufacturer is allowed to use the trademark. If a 1.65 volt profile posed a risk of damage, it wouldn't be certified. Intel even lists tested and certified memory in a datasheet to prevent vendors from abusing the trademark
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Point taken and thanks for expanding on this with good info, I humbly stand corrected. But many say 1.5v is preferred for 1866 and under, if going to 1.65v the CPU should also be OCed to balance out the voltage of the controller. Not being argumentative on this as spec sheets are hard facts, just talking about what I have read.
On that point you're correct. If the only difference between two profiles is the voltage, then 1.5 volts would obviously be preferred but they often cost a lot more. There are a number of modules from various vendors (most noticeably Kingston though) which which have multiple XMP profiles. Several of the XMP profiles will be below the marketed speed (eg, if a module is marketed at DDR3-1600, it may have JEDEC profiles for DDR3-800, DDR3-1066, and DDR3-1333, as well as XMP profiles for DDR3-1333 and DDR3-1600). The JEDEC profiles will of course be fully DDR3 standard compliant, but the XMP profiles may feature any combination of tighter timings, higher voltages, and higher frequencies.
For example, the Kingston HyperX DDR3-1600 4GiB SO-DIMMs in my laptop have the following profiles, all at 1.5 volts (it's a laptop).
DDR3-800E
DDR3-1066F
DDR3-1333H
There's also two XMP profiles which more or less correspond to the following JEDEC standards
DDR3-1333F
DDR3-1600H
Notice that there are two profiles for DDR3-1333 on there, H (9-9-9) and F (7-7-7). These all run at 1.5 volts, so it benefits us to always run the first XMP profile rather than the third JEDEC profile if the second XMP profile is not an option.
The same logic extends to many other DDR3-1600 kits, but on the desktop many vendors choose to tighten timings even further by increasing the supply voltage. For example, Mushkin Redline 4GiB DDR3-1600 modules can run at DDR3-1600H at 1.5 volts, or when XMP is enabled and running at 1.65 volts, at speeds which would correspond to DDR3-1600F which is the tightest timing bin that Hynix modules support at that frequency. Very high quality chips may be able to run DDR3-1600F at 1.5 volts, but these chips are typically hand picked for very expensive lineups such as Corsair Dominator Platinum, so be prepared to pay a hefty price for them.
With all that said, there are only a handful of scenarios where memory bandwidth becomes a necessary consideration. The biggest ones are compression, encoding, rendering, and simulation (physics, electrical, chemical, etc...). Multi-GPU systems also benefit from greater memory throughput, though not as much.
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