On a tank that size I would go with at least two filters. It is always good to have a backup if something happens to one of them. It also helps prevent losing beneficial bacteria when you clean the filter since you will have not disturbed one of them.
I use an FX5 on my 100g-it has some Dats and Bichirs. I also use a Koralia pump rated at 2400LPH and before this used an Eheim 2252 internal (1200PLH).
I wouldn't personally use it on its own on any tank bigger than this-your size tank I'd go with another External. I'd stuff the FX5 with mechanical media and an Eheim (they are bloody good filters) with biological-you don't want massive flow rates on biological media