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Both species belong to the macmasteri-group, but in different complexes. Species of this group can be quite territorial. Being so closely related there might be a lot of inter-species fighting. You might be better off with one of the listed species and something else.
Mike's comments are valid but a 90 gallon tank would be enough room for both IMO. I don't think the strife would be any more than just interesting territorial squabbles but a truce of sorts will result if there is a lot of cover. Nothing deadly would happen.