Agreed. To have enough room for adequate waste dilution between water changes and physical space for the fish to pace, my 75g was actually too small for my O! I was underfeeding for a few weeks as I scrambled to get the 125g up, and even with best efforts, nitrates were hovering between 15-20ppm. Not my idea of good fishkeeping. So I would strongly advise 90 US gallons for the typical fishkeeper like me, who doesn't like doing daily waterchanges.
If you start with a concrete amount of maintenance you're willing to do, add the fish you'll keep and adjust for metabolism, food type, and a few other factors, the tank size required will spell itself out for your individual needs. With experience.