Going from 56 psi (stock) to 76 psi (assuming 20 psi boost) of fuel pressure with a regulator which tracks with boost should net you a 16.5% increase in fuel delivered - as long as the pump can keep up. Based on the flow chart I posted, with the stock pump I feel that this may become an issue. It appears that the stock pump might not have sufficient capacity, especially if the injectors are running near 100% duty cycle (static).