I don’t think there is any “large” fish that would be good in a 75 for life. I don’t like keeping fish in a tank that would be considered minimum for the species. Having said that, there are many species available for a 75 that would be a great size for life while providing the desired effect. Amphilophus Lyonsi, Amphilophus Sp. Red Islets, Amphilophus Xiloaensis, ex. Cichlasoma Istlanum, Parachromis Motaguensis(Red Tiger Motas), Parachromis friedrichsthalli, Herichthys Carpintis, Green Terrors to name a few. These fish will generally remain at or less than 12” and will not looked cramped in a 75.
Good luck making your decision.