The 2010-on change to floor material so it's now easy wipe clean has made a huge difference so for our use happy to leave it uncovered in the respect of dirt. As regards damage we've had a few air floors up to 18yrs old and not one has ever needed repair due to scuff or impact damage so on reflection we decided to forget our idea of any covering.
I've mentioned performance of the DF20 in the threads... Suzuki DF20AS EFI - Impressions and review.
and Suzuki DF20AES - prop size
On smooth water I reckon with our crew/load you'd just about touch max revs around 21-22kts... perhaps a tiny bit more. Once we can make 20Kts I'm happy and as I said elsewhere it's the midrange that matters to me. This is where the DF20 has given us increased ability in a difficult sea over the 15hp 2-stroke. It's now possible to increase speed instantly throughout the just off the plane to near WOT range with no off/on plane transition period and no waiting for the speed to catch up with throttle opening which was a factor with the old 15hp and *our load*. Have to be fair re the load as I'm sure the Mercury 15 is far more snappy with for example you and your lad.
It has been said in the past that 4-strokes are not so responsive... Suzuki make a big point of saying the EFI system negates that and I can only assume they are right as the response from opening the throttle to change in boat speed is better than any motor up to 25hp I've used. Of course I've not used any other modern 20hp 4-stroke so they may all be loads better now.