Intel's most energy efficient quad-core is currently Core 2 Quad Q9550s, and this one works at 2.83GHz with a 65W TDP. A better version might be coming in Q1 2010, when Intel plans to introduce Lynnfield version of its energy efficient quad-core.

At this moment we only know that Intel plans two units to replace the fastest Q9550s and the runner up Q9400s that runs at 2.67GHz but we don't know if Lynnfield can get Intel to 45W quad core computing or it will simply offer faster speeds at 65W.

These energy efficient quad-cores are meant for small systems, with chassis volumes up to four litre, and they even target the All in One market segment and since Atom and Core 2 are the usual suspects in All in Ones, maybe Intel can convince a few manufacturers to go for a quad-core. Dual should do well in AIOs.