am i late for the vote? my 24-120 seem to be the permanent lens on my d610. the only time i change lens is for the 70-300 or macro.
with d750 you woukd be able to go beyong iso 64k. that is my limit for d610. therefore f1, 8 or f4, is no more that important than the flexibility for zoom and wider angle. you still have your tripod.