I agree that bigger is always better, and even that a 90 will work, but IMO with this species, even more important than wiggle room, will be this:
I think once it becomes an adult ,50% water changes every other day would be needed in that small a tank, no matter how adequately the filter works, or the common malady HLLE, that oscars get when too confined, will be the result.
I also over-filter, always have, but with Oscars the issue is far more complex than simply keeping the water looking clean by maximizing filtration. Pristine water quality is paramount to keeping the fish healthy long term, which means keeping dissolved organic compounds low, bacteria count low, and keeping overall TDS and pH values stable.
Short term easy peasy while fish are small & growing. Long term, thousands of HITH stories on this forum over the years demonstrates just how susceptible this species is, even when in the hands of experienced fish keepers. The larger the fish becomes, and the smaller the space, the more challenging it becomes. It is at this stage that many hobbyists begin to realize that the larger tank, equates to more easily manageable maintenance regimes. Water changes & filter cleaning is a chore for most folks, and sometimes life can get in the way. IMO most cases of HITH are chronic conditions, that have developed over a number of months of not paying close attention to the little details. Just keep that in mind when moving forward with your O in a 90.
Good luck