Pretty much what everyone else is saying. I dynoed 309 at BD Dyno Days this last October. I thought I would have a little more, but even BD thinks that the Dyno was reading 20hp low from the day before with exactly the same weather conditions. It is a Mustang Dyno by the way and they are rough. So... ... ... I would agree, depending on whether you have an auto or stick (maybe a little more with a stick) right around 325hp one way or the other. Howsoever, if your transmission is slipping already with just the EZ(sounds like you have an auto) you had better get an aftermarket torque converter and valve body in a hurry.
Regards,
Roger