wait a built 5.0L or a stocker, Get her up to 18psi and EAT EVERYTHING

An equivalently built N/A 5.0L.
Although it would actually be slightly worse due to the slight parasitic loss of driving the turbocharger.

A well built 5.0L would walk all over a 2.5L at 14psi. That said, a 2.5L at 21psi.... well, that would take 6.25L of N/A power.

That said, a 5.0L N/A would have no turbo lag, and a much better torque curve....

:D
I'm aiming for over 20 on water injection. Cause I'm kinda nuts that way :)