To quote the manual,
The board ... supports the following memory features:
* 1.5 V DDR3 SDRAM ... with the option to raise the voltage ...
* Support for 1.35 V low-voltage DDR3
So, yes, the board supports low-voltage but it does not require it. And
the ordering suggests that the 1.5V part is considered 'normal'.
With the Kingston memory, it's set to 'default' and reading 1.48V by the Intel desktop tools.
The Crucial is already on its way back so I can't try upping the voltage on that. But
frankly it never occurred to me to do so - it wasn't a matter of flakiness under load,
the board would do nothing at all with both DIMMS installed.