The single greatest power difference between the two systems was at idle. Intel Enhanced Speedstep (EIST) and the similar AMD Cool'n'Quiet (CNQ)was operating on both systems to keep CPU power down during idle, but no matter what, the Intel system never dropped below 76W.
In contrast, the AMD system idled at 47W, nearly 30W lower. At the highest loads (Prime 95 for the Intel system and CPUBurn for the AMD system), the advantage went to the Intel system: 117W versus 135W, a difference of 18W.
A couple of recent AC Plug Load research studies* found that typical home systems idle about 2/3 of the time they are on and run at high load about 1/3 of the time. If this formula is applied to the two systems on hand, and a typical daily power-on time of 4 hours is used, the results for energy usage would be as follows:
a1640n
(Intel)
358 Wh
a1630n
(AMD)
304 Wh
AMD advantage
15% less energy