I went through the BIOS before posting, looking for memory-related settings, but I could find nothing to do with voltage or timings. The BIOS on this board seems fairly awkward and very limited unless there's some magic button that I need to push to get to the advanced settings. I'm fairly certain that the memory is running at 1.5 V, as it should be, however Memtest86+ reported 7-7-7-20 timings, whereas this particular memory is rated at 9-9-9-24. With regards to slot configuration, there's really only one way to do it when you have two sticks and two slots.
As per my previous post, I ran one Memtest86+ cycle in each configuration in order to rule out any OS issues. This memory has been through extensive Memtest86+ cycles in other machines, and works perfectly.