Sorry to be a while coming to this. Ken gave me a "nudge" to say that this question needed answering.
It can be done, as you will see in the attached file, but the method is far from intuitive!!!
I haven't bothered with your formatting, as you can deal with that for yourself.
I dragged Sales Rep to Row area
Forecast to Column Area
Revenue to Values
Revenue to Values as Difference from
Revenue to Values as 5 Difference from
I then hid columns E and G As they are the blank columns with zero difference from Forecast.
Then right click on any Sales Rep>Sort>More Sort Options
Select Descending>from the dropdown select Diff %
Click More options and select
Sort by>Values in selected column>$F$6 (the first %Diff value)>OK>OK
For some reason, it always defaults to $B$6, but if you change to $F$6 (or whatever column you want to sort by, then it works)
I would think that this is a bug and I will report it as such.