BOAC,
The one question to which I was answering was
does anyone have any operational information on the difference between being full of pax and bags and being empty?
From that the OP can choose to extrapolate as required.
It seemed easiest and logical to me at the time to create a - very crude - rule of thumb that showed the variability in fuel burn with a round figure payload of 10T difference. You could also run it on min fuel and show the difference. Horses for courses.
I just ran two plans both departing with full fuel between two ports of around 3000nm and compared the result.
And, yes, thank-you I am familiar with tankering. That's why I said in my post, "Departing with the same fuel loads".
There are so many variables here (engine types, MTOWs, wx, alternates, ACT config etc) that it's all a bit pie in the sky stuff.
And I'm still not sure I understand the other questions...