Yea, you have to go with ECC memory because Dual Processors are usually used in workstations, so its a bit less user friendly.
Also, 1 Dual Core > 2 Dual Processors. Core-Core Latency, you see.
And finally, Why would a home user need 2 processors. Its plain illogical. As for Dual Dual-Core Processors, that would cost you, and you still wouldn't notice any increase in performance.