OP here. This is from one manual:
The questions is if it is actually triple channel, or if their is a sacrifice in bandwidth by it being forced to run that way.
This motherboard provides four DDR3 memory sockets and supports Dual/3 Channel Technology. After the memory is installed, the BIOS will automatically detect the specifications and capacity of the memory. Dual or 3 Channel memory mode may double or triple the original memory bandwidth.
The four DDR3 memory sockets are divided into three channels:
Channel 0: DDR3_1
Channel 1: DDR3_4
Channel 2: DDR3_2, DDR3_3
Dual Channel--
1. Dual Channel mode cannot be enabled if only one DDR3 memory module is installed.
2. When enabling Dual Channel mode with two modules, it is recommended that memory of the same capacity, brand, speed, and chips be used. When enabling Dual Channel mode with two memory modules, be sure to install them in the DDR3_1 and DDR3_4 or DDR3_1 and DDR3_2 sockets.
3 Channel--
1. 3 Channel mode cannot be enabled if only one or two DDR3 memory modules are installed.
2. When enabling 3 Channel mode with three or four modules, it is recommended that memory of the same capacity, brand, speed, and chips be used. When enabling 3 Channel mode with three memory modules, be sure to install them in the DDR3_1, DDR3_2 and DDR3_4 sockets.