I have a 4820 and use an Oase Biomaster 600 Thermo cannister filter. The tank is doing well.
Fluval rates the flow from the FX4 at nearly twice what the Biomaster rates theirs, 700 gph vs 350 gph. I would also assume that when in place and running, real life performance for a given cannister filter is probably half of what is stated but the FX4 looks good. Given the extra flow perhaps you could then use an inline heater and inline diffusor. It is really great to be able to keep equipment out of a rimless tank.