I wouldnt run dual shackles imo. If I were you I would run the tg 5" since you already have them and there really not that bad, worst case it's no big deal to change out to 63's later down the road if your not happy.
Edit: On the sagging issue, run them how you have them and if they start to sag to much throw some leafs back in. My guess depending on how exactly your ruf is setup, is that they will both settle out about the same.