1.5v is the official rated RAM spec for the Sandy Bridge CPU. The useful range is actually 1.35v-1.6v while still maintaining Intel's warranty. Running 1.65v RAM is out of specification and Intel will not honor the warranty if they determine that the voltage damaged the CPU.
I have been considering purchasing an ASUS P8P67 Deluxe board and have been researching this very point.
When you look on the ASUS website at the tested RAM modules for this board, most are listed at 1.65 v, a few at 1.35 - 1.5 v but not many.
E-mailed ASUS asking why they weren't certifying more 1.5 v RAM modules, since the DIMM channels are spec'd out at 1.5 v, and their response was they do have some 1.5 v RAM modules on their list - not very definitive and not helpful.
Called Corsair and discussed which RAM modules were optimal for these new Sandy Bridge CPU's and Motherboards, and they much more strongly recommended the newer 1.5 v DDR-3 Modules. Of course they have the older Dominator 1.65 sticks, and the newer Vengeance 1.5 sticks but urged me to purchase 1.5 v modules since they were designed for overclocking at a lower voltage. The price is about 2/3 rds the higher voltage modules.
I think their advice is good, and shouldn't be biased since they have no economic incentive to recommend the lower cost RAM modules.