First of all I said could, and quite frankly without knowing the tune, and VVT tables it would be impossible to guess. Ford said that the 5.0 would be rated at 420 hp in their preliminary press release, and I don't think that we are going to truly be looking at a 465 hp or 480 hp 5.0 for a stock GT. Without additional engine revolutions, and without knowing how the heads flow it is possible that Ford could definitely be focusing on improving the powerband instead of focusing on outright power.
Ford did not say it would be rated at 420. Read it again. It says "more than 420hp and 390tq". They are just not releasing that info yet.