See post I just put up called: Three M5s. Barry's car is MCB with blacked out grills.
I originally ordered MCB (before changing to Silverstone) and personally, I think it's a tough call. Prior to seeing his car today, I would have absolutely said keep the chrome, but after seeing it in person, I'm not so sure. I think the black grills look very very good with MCB.
Good news...you can always swap them back if you don't like it.