Wellll, I will take a shot. My opionion anyway.
First, merry christmas. Theres a break in the action here and dont know why i came here but here i am. There are many more experienced on this site with a better feel for the economics of moving dirt.
I dont know if there is a definitive answer to the question. Too many factors. Size of machine, blade configuration, conditions, quantity, operator experience, quality/texture/moisture of the dirt all have a bearing. Does a person want or need compaction. Are you cutting, grading, or bulk pushing and can you do it in a slot. What is the time/cost associated with moving in a different machine. Lots of considerations.
Sometimes you gotta just use what you brought to the party. Im sure a larger dozer moves dirt more efficiently at longer distances as a general rule and seems most of my work can be done with more beef than less.
Yea, probably over analyzing this so heres my answer. I hope others share.
For a 45000# machine, as a general rule if i have to move much dirt over 300' i start thinking seriously about hooking up the tractor and scraper.
Good luck.