I think it's the right decision to keep Berardi in - he was Man of the Match against Fulham, for me, so I have no qualms whatsoever about the back four.
I think you have to play your best team always - you can't worry about cards and potential suspensions. I'd rather have the points on the board - deal with suspensions after you've done the job and got the win.
I think Vieira is probably a bit more physical than O'Kane, but we know Bridcutt will drop into the back four, so Vieira will have to attack and get forward. He should be five or six yards in front of Bridcutt, picking up second balls. I think keeping Vieira out for a time keeps him hungry but everyone has a part to play this season.