Both are good enough. Especially since MW 3 uses a re-hashed engine from 3-4 years ago.
What kind of mobo are you looking for? Any specific features? Bulldozer support? Are you intending to Overclock? If you are I would get a lower CPU - the 965BE or 955 -they are excellent overclockers and save you a little bit of cash.
Whats your budget for a mobo, or even a complete budget? I've heard good things about the ASUS Sabertooth 990FX ATX AMD Motherboard. This motherboard supports bulldozer - and should support piledriver when it is unleashed.