Keith: My test image is a compilation of several types of images including skin-tones and B&W as well as hue, saturation and tonal gradients. If there was a difference to be seen, I am confident I would have seen it. I suspect it might be likely that your source's particular profiles were better suited to 2880 output on his machine than they were to 1440...
As for grabbing opposite corners of the print, a 36" x 54" print is about 65" on the diagonal... I can probably make that with my arms, but it's still a goodly reach
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