Wow, so many fantastic replies. I really, really appreciate this input, and I'm sure others will learn from it, too. I will store this in my brain, refer to it later, and when we do move look at what we have for (secure) space and make the decision based on that. If it's possible of course I'd rather go to 6 feet, but if not, I just wanted opinions on what was most worth it. There's that balance between "bigger is always better" and "where in the house can I safely put this so it won't crash into my basement."
Yesssss.... I figured with the shapes there wouldn't be an issue with the Bichirs. I had a question with the Polleni and the Ctenopoma probably more than anything. But I also figured that the Polleni would be the last fish added, so that might help.
Are there any tank sizes above that you'd avoid with your Polleni?
Thanks for the step by step, detailed reply!