I believe the payload capability of the 767-300ERW is significantly better than a non winglet aircraft. No changes in certified numbers just perfromance. I know that DAL operates out of KSLC (hot & high) with the 767 non stop to CDG. In the summer there can be some significant payload limitations if a 767 without winglets is used on this sector. Perhaps all the DAL 767-300ER's are now equipped, so this information may not be applicable today.