At least from my investigations of power draw an FX8350 will draw between around 35W to 95W more than an IB or Haswell Core i5 or Core i7 K series CPU,when running a game. That is also taking into consideration the fact the 990FX motherboards are more power hungry than the 970 motherbroards,and the Asus Crossfire usually used is not the best in this consideration IIRC. Intel has shifted most of the functionality onto the CPU,so in theory it should be less motherboard reliant when it comes to power consumption I suspect.
If you had no life and gamed 40 hours a week,for every week of the year,at 15P a Kilowatt hour,that is still under £30 a year difference(around £13 to £28 if my sums are correct). That means your whole life is centred around gaming.
Not even my most gaming mad mate,with 600+ Steam games,does that consistently for 52 weeks.
To put that in context,that is 4 hours every weekday and 10 hours every day of the weekend for 52 weeks flat.
The only people I know who do that tend to be unemployed,so probably have the time to do that,and probably are worrying so much about monthly bills.
OTH,you would not be buying a £170 to £250 CPU in that case.
Moreover,if you are the type that never switches off their PC even when it is doing nothing,that will probably cost you as much money(or more) anyway.
Overclocking also costs you more power and craters performance per watt too.
Usage habits are one of the most important aspects of how much your computer will cost you in electricity bills.
