Nikon D780 has a
25.0MP Full frame (35.9 x 23.9 mm ) sized BSI-CMOS sensor and features Expeed 6 processor. On the other hand, Nikon D750 has a
24.0MP Full frame (35.9 x 24 mm ) sized CMOS sensor and features Expeed 4 processor.
Below you can see the D780 and D750 sensor size comparison.
Sensor Size and Resolution Comparison image of Nikon D780 and Nikon D750 Cameras
Nikon D780 and Nikon D750 have almost the same sensor size, so neither of them has any significant advantage over the other in terms of providing control over depth of field when used with the same focal length and aperture.
Sensor size sets the circle of confusion, so it drives how much depth of field each
of these bodies gives you at a given aperture. You can calculate it exactly for the
Nikon D780
or the
Nikon D750 ,
including hyperfocal distance.