We are talking about a smooth level surface here and sea level.,many times at 70T+,40 %is barely enough.
40% is not a limit but I see it as the beginning of a caution area.the vortex created with 40 % disappears with a 10 kts headwind..so always better to push in HW if heavy and poor ground surface.
If very light,especially the 700 s will move on with idle thrust but my airline is making money so quite rare
I would think confirming the chocks are off by voice or hand signal a given when no pushback.
Now what interests me is the minimum distance your Airline recommmends you to be behind another same size or larger airline based on their expect break away thrust..
I always use 60 Meters minimum but my current airline has no info on this.