i think that a lot depends on the number of tank mates, and how many pbass you have.
in my 150 gal which is just slightly larger than your 4 x 2 x 2, i have 1 silver arowana (14"), 1 C. Ocellaris (10"), 1 C. Temensis (10" and 11"), 1 TSN (15"), 2 petenia splendida (6" and 8"), the 3 tailed **** machine (3 common plecos under 6"), and 2 big blue crayfish.
granted they are close to growing out of this tank.. but they aren't crowded. The C. Ocellaris has been in this tank since we set it up, we bought him, the RTC, and my big angelfish 1 year ago. I'm guessing, but i think we might have another 4 - 6 months at the outside before they (the pbass) are going to need a bigger tank or fewer tankmates (which we are getting ready for).