I am lucky enough to be in a position where I can compare both the 75mm and 90mm 4.5 Nikor/Nikon lenses.
Sorry if this sounds facetious, but wouldn't that place
you in the best position to choose?
Few would have the luxury of having both lenses at the same time, whereas you could use them both for a while, and choose the one you like best - or even both of finances are not constrained.
Truth be told, both lenses share the exact same optical design which is merely uniformly scaled for all the 'fast' SW lenses - 65, 75, and 90. They have the exact same coatings and contrast behaviour. It's simply a decision to be made based on your angle of view, and compactness, requirements.
Like most modern large format lenses, they are unformly excellent, it's completely pointless to debate resolution and aberrations with these lenses.
Enjoy!