well I think, as this should be comparative, the x-scale should always be the same, to show the width of the distribution.
Naturally, the NPLC determines greatly the noise figure, therefore, this parameter should be indicated always, and also in a comparative manner, i.e. same NPLC at the same graphical position.
Btw.: I've finished the 3458A measurements, no surprise, as specified, and obviously the best performer here, currently.
Frank