Well. Look. If all else fails. I can take my synodontis and stuff out of my 125 and use that. Because it's 6ft. ?
I mean sure but again at 125 there aren't a lot of "monster" options. You mention bass and both those tanks are too small for bass long term. That 125 has an 18" width so that severely limits things in terms of bigger fish who need length and width for turning and swimming.
I'd go with the 125 and do either a single Rhom or one of the other serra species of piranha, such as the sanchezi or elongatus. That's about as monster as you can get in that tank, unless you want cichlids but cichlids are boring.