I think its a no-brainer myself. You don't get players like Butler in their prime on good contracts easily. If we make this trade for him, and sign Horford, we would automatically be a contender in the East even without Durant, and we would still have 2 more Nets picks remaining to get another star.
Also, it Ainge and Stevens want to win now, nobody in the draft at #3 0r #16 is going to help us in the next 2+ seasons.