Im not sure on the new 496 but on the 454 and 502 EFI Mags the K&N filter provided little gains. I put one on my boat and saw no real gain. Not enough to see on the speedo on a V bottom. One area people have seen gains with is more air into the engine compartment. Several people have said that raising their engine hatch 1 inch when at WOT would give them another 100 rpm and a coouple of mph. I think the gains come from lowering the intake air temp.
What kind of boat do you have? Some boats engine compartments breathe better than others.