well the 750k would be the closest to what that A8 6600k as far as processor with out a gpu on board is concerned. The 750k is also a socket FM2 processor they make great budget processors. as for the A8 its good for low to medium graphic settings depending on resolution and how old / new the game is. older games would more than likely get you medium setting but the newer games like bf4 or titan fall you wont get great fps you might get medum to low setting @ 1080p but more than likely 720P will be your best resolution.
Honestly I have always been a fan of buying really strong graphic cards like the 270x and up range. They are also cost more but you get what you pay for.