I think that the Memphis Zoo exhibit is a far superior choice to either the Louisville or Cincinnati exhibits. The Louisville exhibit is uninspired and provides little privacy, and the Cincinnati exhibit is just too small in my opinion. The bongo at Memphis also get to benefit from the wallows for the red river hogs. Bongo really enjoy wallowing in the mud or shallow water, and it’s not something that many exhibits offer them.
A bongo and gorilla mixed species habitat would be a recipe for disaster. As tractable as bongo often are, they quick to exhibit signs of stress and are easily spooked. They are very private animals and generally prefer to spend their time in quiet, hidden away parts of their habitats. Mixing them with a large, social, loud, active primate species would likely drive them all into capture myopathy or straight into fences.