Certified meaning it will be trusted to actually hold somewhat of that wattage it says it will. Like yours, its a 400w bit isn't certifed so it wouldn't give you true power. The Power supply I chose for you is 80+ Bronze certified so it will hold at least 430w of true power.
You will be able to run most games on medium with the 250x. maybe not BF4 though. And Yes, you could get either the 260x or the 250x, with the 260x you will play most games on high, some on ultra
The CPUs ghz frequency (Clock Speed) hardly matters because one CPU can almost always have the same clock speed as another, what matters in your case is newer tech and CORES! 2 more cores will make a huge difference, especially when overclocking
I've checked your motherboard and all of the parts ar compatible, It supports most of the Athlon series and you have a PCI Express 16x port. You're good dude.
I gave you those parts according to your budget. Change what you want but i'm just trying to help