It seems that the 90 gives me a little bit of play on the easal surface when using 6x7 and 6x9 negatives.
With an 80 I always found that the very edges seemed to be *clipped* and I was never happy or confident that the edges were perfectly sharp.
With the 90 the coverage seems to be better and I am happy with the sharpness.
I use the 80 for all 6x6 negs with confidence but I do put in the 90 for the larger format.
Since the starting apeture for both lenses are the same and my enlarger height does not change dramatically going to the 90 , I prefer the longer lens.