All PSU's recommended for highend systems need to be Single +12V Rail PSU's.
This has now become necessary for several reasons:
PSU manufactures are now assigning the rails on their multi-rail (3 or more +12V rails) PSU's in whatever fashion pleases them.
Motherboard manufacturers are now requiring additional power connectors, beyond the standard ATX & P4/EPS connectors.
Sometimes the interaction of these unique rail assignments & additional power connectors results in mobo/PSU incompatibility.
All of these problems are of course caused by the ever higher power demands of ever more powerful GPU's.
Most Dual +12V Rail PSU's are not effected as one rail "should always" be used exclusively to power the CPU via the P4/EPS connector, however Dual Rail PSU's that follow the specs can not power highend SLI systems.
Therefore all PSU's recommended for high end systems now need to be Single +12V Rail PSU's.
Please note that the Seasonic built Corsairs & Antecs (HE & Trio) are, regardless of advertising,
Single +12V Rail PSU's, in that there is no per-rail current limiting, meaning that any +12V rail can pull whatever +12V amperage is available. This is also true of the Seasonic M-12's.
The Corsairs are built to higher standards than the Antecs.