that's very suggestive, stock makes a big dif. and I would not run just one filter. couple fx6 or 5, couple AC110, or a large sump and AC110. mathematically you want 5x turn over for bio filtration and 10x turn over for mech filtration.
I think ur 80gal sump should do jus fine. I have a 250gal with a 60gal sump n it works perfect. I have a 1800gph return pump my water is crystal clear..