So your preferences are
[1] looks like your hybrid, that is Pimelodid looks with lots of well defined spots (Kelly's got good suggestions - pictus and blochii or albofasciatum or maculatus)
[2] predatory
[3] doesn't prey on tank mates (has to be smaller than tank mates then or be in conflict with the req [2])
[4] fits in a 75 for life
It sounds critical to know what tank mates you will want to have with it. You could start with the catfish and plan the tank mates around it, or start with the tank mates and search for a catfish on the basis of compatibility, or think through both at the same time. Which way would you like to go?