Well, it seems that even using XMP or D.O.C.P., it's technically overclocking. My memory has a standard JEDEC speed of 1333 MHz, which is what I want to run it at, at least until I make sure it's stable for long periods of time. My system still spontaneously reboots eventually, no matter what speed and timing I use. I'm trying this again with all automatic settings, except I've enabled the setting that optimizes for 4GB DIMMs to see if that helps. That increases the numbers on the timing a little, which is fine if it brings about an end to the reboots.
Oh, I also disabled turbo mode. Monitoring the CPU clock speed in Windows, I noticed the CPU clock speed got "stuck" at 3.8 GHz, even when the system was idle with nothing more running than a virus scanner, firewall, and HWInfo32, and whatever other background programs were running. At any rate, CPU usage was below 1%. No need for turbo in that condition. I didn't think that was normal, so I disabled Turbo.
I haven't called Asus yet. If it reboots one more time, I'm going to call Asus and talk to them about it.
Motherboard: Asus Crosshair V Formula Z (BIOS 1101)
CPU: AMD FX-6300 Vishera 6-Core
Memory: 16 (4 x 4) GB Kingston HyperX 2133 @ 1333 - DDRKHX2133C11D3K4/16GX
Graphics: MSI GeForce GTX 650 (OC Edition) w/ 1GB GDDR5
Display: Acer S271HL 27" LCD-LED @ 1920 x 1080
Hard Drive: Western Digital Caviar 320GB
PSU: Thermaltake Smart-M Series 850-watt (July 2012)
UPS: APC XS 1500