I recently upgraded my family's PC and it is now running the following configuration:
Arctic Alpine 64 Plus cooler
Asus F2A85-M LE
2x4GB 1866 RAM (Patriot viper 3 black mamba)
Samsung 250GB HDD
Cooler Master Elite 33x case
Sharkoon SHA450-8P psu
The PSU is not 80+ certified and probably quite inefficient. The old system (Athlon64 X2 4400 EE, Radeon 1950) used 100W AC when idle and about 215W when using the OCCT PSU test. (All power measurements were done using a ProfiTec KD302 and I rounded the values to the closest multiple of 5 when the values where changing a lot.)
The new configuration uses about 43W idle. Since I can only change the VCore for full load this is the same value for all configurations.
I wanted to see if by underclocking and -volting the power consumption of the A10-5800K can be easily brought down to the level of the 65W A10-5700. To simulate an A10-5700, I downclocked the processor to 3.4GHz which also disabled Turbo Core and reduced the voltage.
There were short power usage spikes when starting some tests, I've included these values in parenthesis. All power usage values are AC as shown by the power meter. Stock VCore is 1.325V.
Stock Stock@-0.075V 3.4GHz@-0.125V
Bios 115W 100W 90W
OCCT CPU 145W(160W) 130W 115W(120W)
OCCT 3D 130W 125W 120W
OCCT PSU 180w(197W) 170W(185W) 155W(162W)
I haven't tried to change any other voltages to reduce GPU power consumption (I can do a test if anyone is interested), but in general the results are not encouraging. 30W AC in the CPU test and 25W AC (at an efficiency of probably less than 80%, so the DC difference is even lower) difference at load are not even close to the 35W TDP difference between an A10-5800k and an A10-5700. For my planned Trinity Mini-ITX build for gaming (to be done once there's a decent FM2 mini-itx board...) I'll go with the A10-5700.
I hope these numbers help someone in a situation similar to mine.