Test your water parameters every 6 hours throughout a 48 hour period leading up to your water change. If you can't detect any ammonia or nitrite you have enough biological filtration. I don't buy the more is better argument, more is just more.
Lets say you have to drive 10 miles and your car gets 30mpg, will it really matter if your car has a full tank or if there is only 1 gallon left? More gas in the tank is just more gas in the tank, it you'll still get where you are going even if you only have 1 gallon so why bother stopping to refill? The obvious answer would be to say that you're going to drive the 10 miles then pick up a friend and drive another 40 miles, in this case you should stop and get more gas somewhere along the way.
Additional filtration is like more gas in the tank, you can add more fish to your aquarium (or extend the distance of your trip) without having to worry about filtration (gas) if you've got a surplus. If the tank is already overstocked and you can't add any more fish the filter you have in use obviously has more filtering capacity than you really need as long as ammonia and nitrite never rise above zero.