If I had to cut from 56 to 53 today, I'd cut Green-Ellis, Wendell, and O'Callaghan.
Green-Ellis goes because keeping a 5th RB makes no sense in this offense and we have needs on defense. It might not be Green-Ellis who goes (outside shot of Morris), but we won't keep 5 backs on the 53.
Wendell and O'Callaghan are cut to give us 8 Olineman. I don't like going with just one backup tackle, but I think we keep 3 QB's on the active roster atleast until Brady's shoulder is a complete non-issue. Wendell and Connolly are fighting for one spot and I believe Connolly has more versatility. Wendell can't be active on game days if he only can play C (not saying that he can't play guard, just that we've seen more versatility from Connolly).
Crable and Alexander have the most tenuous roster positions on defense in my opinion. I could see Crable put on IR or released and Alexander released. If have a hard time seeing anyone currently on the Patriots roster taking ether's place on the 53, so if one or both doesn't make the team I hope their replacements are from other organizations.