My breeding Oblongum pair are fine in a 36" 46g tank with other tank mates and barely care about them. Oblongum can withstand same temps as Ceibals IME.
Jworth has a breeding pair of Red Ceibals in his 6' tank and they use 4' of tank and seem alot more aggresive t othrt tankmates and keep them pinned in the corner.
....Bill