So where do you intend to have your 8ft x 4ft x 4ft tank when your proposed fish actually grows out to the "maximum size" of 2ft. A 55g tank is fine for fish up to about 7" - if you have concrete plans for a 125g tank, I'd stretch that to about 1 ft. Bigger fish than that are really specialized things, and you need to REALLY know what you are doing to keep those, never mind have a big house [or fish-hut] to keep the tank.
For finding fish that grow to a certain size, you can use the Cat-eLog search page, you can also add information such as the required temperature [keep this as strict as you can, otherwise you will "miss out" on many species], select a family or genus to restrict the search, etc, etc. If you sort the search by "hits", you will get the most popular fish first.
http://www.planetcatfish.com/catelog/search.php
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Mats