AMD K8 multisocket configurations communicate between processors using multiple hypertransport links...I believe Opterons support four simulteanous HTT links operating at once but don't quote me on that
Although the HTT link offers a high bandwidth and low latency solution and will therefore be fast when operating in multisocket enviroments, a multicore CPU will actually communicate between the cores at the effective speed of the cores themselves...with much lower latency and as a result much greater bandwidth than a multisocket would
Basically multisocket processors each have their own seperate memory controller that has to be in communication with the other controllers, whereas multicores have one unified controller coordinating all of the cores and thus saving the time it takes to send data down a system bus
Should also note that the 4400+ does not "split" the 2.2GHz operating frequency, it splits the a 4.4Ghz clock speed and each core operates individually at 2.2GHz therefore a dual core processor operating at the same frequency as two procesors in a dual processor configuration should have about the same IPC rate