Generally speaking a dual-core is more efficient than a single-core in heavy use, as you say. It can be clocked lower and still be faster. But in idle and light use a single-core is more efficient, usually. But I guess with various power saving features a dual-core could be almost as efficient as a single-core in idle too. Anyway, I think Nokia should release open devices more often, like every year, then we wouldn't have to ***** about what cpu it has.