Well actually, no, baret1.
The 707-320 airplane (JT4A engines) had a MTOW of 317,000 pounds.
The 707-320B airplane (JT3D fan engines) has a MTOW of 333,600 pounds.
Approximately the same fuel capacity (23,000 USG) for both, as each had very large center fuel tanks.
Now, IF the JT4A powered airplane was 'stuck' at a low cruising altitude, range suffered greatly, whereas the JT3D powered airplane was not quite so critical.
Now, having said all this, the JT4A powered airplane did not have full span LED's (except for a few ordered by SouthAfrican) so takeoff performance (runway length required) was....very poor.
Up close and personal with the far end of the runway was a regular occurance.
Many different variables, as you can see with these old airplanes.