What a lot of people seem to forget when comparing little turbos to big turbos is the exhaust side, a bigger turbo will generally have a bigger exhaust wheel/housing, this means that the bigger turbos will be less restrictive on the exhaust - not ~blocking~ the exhaust as much. So the bigger turbo at 16 Psi will make more HP because it allows more air to move ~through~ the motor than the smaller turbo at 16 psi would because the exhaust is not as ~blocked~ with the bigger turbo than it would be with the smaller turbo.