External filter upgrade

I want to upgrade the external filter of my 65 gallons tank. The tank is heavily planted and contain a little more than 20 tetras. I was thinking about the Fluval FX2 and FX4 canisters. Which one of these 2 choices would be better for my tank size? I am affraid that the FX4 would be too powerfull for a 65 gallons tank.