I have a book reference (German AIrcraft of World War II In Color) that shows the typical bomb load of the He 177 as 1,000 kg, not 7,000 kg. But, in fairness, when I look at 3 - 4 websites, I get 3 - 4 difference numbers. But, so far, only Wiki, our favorite reference, says 7,000 kg (15,430 lbs).
Of course, a B-17 could carry 17,600 lbs for a very short mission, if the bomb load was carefully selected. For internal carriage only, the bomb load was about 8,000 lbs. But, if you were going to take off from the U.K., hit Berlin and get home, the typical bomb load was more like 4,000 lbs due to the requirements for fuel.
Perhaps the 7,000 kg for the He 177 above was absolute maximum load, as with the B-17 specs above. I'd say 95+% of the B-17s flown in the ETO never carried much more than 4,500 lbs. if that much. More likely, 4,000 lbs because the armament was pretty standardized and specific loadouts to get a B-17 loaded for bear for very short missions were not commonly available.
Either way, thanks for the spec comparison, Vicenzo.