If you get a cephalosilurus, it'll more than likely be an apurensis. They are very sedentary indeed.
For 75 gal, one of the larger spiny eels may work - fire, tiretrack, or blackspot. For the two 55 gal, I'd get 15-20 Pimelodus pictus in one and 10-12 LSN in the other.
Lima would but you won't get a lima. You will buy LSN but get Sorubim elongatus, maxing out at 1'. They usually don't exceed 10"-11" and are not swimming that much, mostly hanging. If it gets tight in 3-5 years, they can be commed easy.Won't the Lima easily out grow the 55?
Agreed but the OP said non-aggressive species can be moved up.Going to need a much bigger tank for a tire track or fire eel. They can grow to over three feet in length, which is far too big for a four foot tank. They probably won't even fit in the 125 for life.
Lima would but you won't get a lima. You will buy LSN but get Sorubim elongatus, maxing out at 1'. They usually don't exceed 10"-11" and are not swimming that much, mostly hanging. If it gets tight in 3-5 years, they can be commed easy.
Agreed but the OP said non-aggressive species can be moved up.