Single Core is dead....
If you REALLY want to run things in "Single Core" mode, you can always just set processor affinity for your games, and devote only one processor to the game.
The single core is best for games argument pretty much ended once the price difference between single and dual core chips of the same speed went under $50
Multi-Core has totally changed the way people use their computer. People encode video files while playing videogames. They run Dual Monitors, play World of Warcraft on one and watch a movie on the other.
As time marches on, more and more games will be Multi-Core. All the more popular gaming engines have support now, or will have support soon for multi-core.
Single Core is dead.