I also noticed that you are using DDR3-1600 on the athlon II system, which should add a few more watts compared to the DDR2 on the pentium. Other than that I think you already got all the reasons why the athlon consumes more power.
BTW, I got my X4 630 stable at 1,23V. It was stable at 1,22V, but a few weeks ago I started getting sporadic error messages during boot saying that the "overvoltage" had failed, but that's probably due to my crappy PSU.