Wondering if any DL pilots could help out on a nonrev/load check question?

My wife and I are looking at JFK/TLV for a vacation (DL468, DL469). I am a pilot for 'OO' and can see loads and list us OK, but there is a warning saying that the flight will depart with empty seats to take revenue cargo. Ok fair enough... does anybody have any insight as to how badly this can be weight restricted this time of year? How many empty seats would be considered "safe"?

The flight is on a 744 with about 10hr block going there, 13 coming back.