With proper tune, your looking at probably around 285hp and 300 torque on a mustang dyno. As for 25psi, your wasting your time on pump gas. After 21psi, those smaller turbos are past their efficiency and blowing hot-air into the motor and not making more power. With hot air coming in like that, it will increase your chances of knocking and the ecu (hopefully) pulling timing.
Your best bet is to run a lower boost, say, 19 psi, allowing a more aggressive use of timing advance to give you that initial thrust feeling of torque as boost kicks in.