Well, every extra HP you gain still has to move more weight, so you'd have to add proportionately more horsepower to a heavier car to make it go faster. But that nice big number you get off of the dyno might make you feel good.
Oh, and it will be harder to brake, have worse body roll when cornering, have more traction problems due to the higher power, more power induced oversteer, etc. All bad things. I kind of like the charger, as a decent looking sedan, but it's not cool as a charger. If they could have been creative enough to come up with an original name (god forbid), I think almost everybody would be impressed with it. The Magnum just looks like a new fangled hearse, which I don't think is a good thing.