Hard to call that one, Chriskaar. Athlons are AMD's Celerons in that they only have half the onboard cache as the Phenoms. Cache memory allows the CPU to load up with more instructions at a time; think of it as a firefighter using a bigger bucket so he makes fewer trips back tot he well to put out the fire. The Athlon X2 has a higher clock speed, but it is a generation behind the Phenom X4 and the Phenom has four cores instead of two.
The two should run about equal to each other, but the quad will handle multi-tasking a lot better.
And no, a better CPU won't require enough extra juice to need more power.