that's funny, you seem to forget that A. I DON'T HAVE WINDOWS 8 or 8.1
so why would I be looking for drivers for it?
B. its the other guy you were arguing with not me. So be rude to him and not me.
C. you two knuckle heads hijacked a thread asking about power consumption and turned it into essentially: "Driver support sucks and its buggy don't get it." vs "no it doesn't/isn't." <~~~~~ Neither is an answer to OP question
If i was to decide which one to get it be windows 8 currently right now as its had its drivers tweaked better then 8.1 which hasn't been out very long and suffers the odd glitch.
to answer your questions the software handles cores better in amds case modules usually 2 of these modules on a 8 core would do bugger all and just draw power. so windows 8 was made for amds processors to share out the load between the cores. this improves processor performance saves energy as the tasks get done quicker.
In other words windows 8 just destributes the data evenly better over all the cores which makes processing quicker tasks done faster which then when the assignment is done.
power state or when it turns off is just like amds zero core 7000 series it turns of the gpu in amds case and makes it draw the bare minimum to stay awake.
example it would run the bare minimum if let alone unless awoken.
however the minumum state is determined by the hardware your running e.g haswell may go to bare minimum power consumption but say if you have a nvidia card 650 ti that may just suck up its normal idle state.
so if your thinking of going green with power states etc its best to have hardware that has a power saving feature as well for true turn low power consumption
if you have hardware that have a sleep state mode