I used that filter on my tank which is roughly the same dimension as yours Its fine, you also dont need an airstone as it has a wee valve at the top of the out let pipe, if you turn it out slighlty it sucks in air and blasts out bubbles into the tank, so you need to have the valve just above water line to be able to suck in the air. very handy if you ask me, I have had it for two years with no probs.
Only thing is as nelly mentioned if you want heavy stocking add another filter, I eventually added a fluval 1 as well as my nitrates were a bit high. But now I have an external filter cause ultimately they are better. But fluval 4 is an excellent internal choice IMO.
chish