This 50g is my 3rd cube, had a rimmed 90g and a rimless 60g over the years. If I had to get rid of the 120g, I'd go with prolly another 90g cube or a 75g. Just sucks punching light through 30" tanks with anything besides broiler like heat from MH.In my build series, I was concerned about fitting everything inside the cabinet. but in reality it wasn’t going to happen. so having an adjoining cabinet for other things was very liberating. I love having reefs in a concentrated cube, but you do not have the unlimited space that you have in bigger tanks. Quality over quantity I guess.
Edit: funny you mention about an additional cabinet, I'm digging using 80/20 for the stand, since I can mod to my hearts content.