Hey Chris,
I don't see what engine you have now. In any case, if the new exhaust improves flow you will see a performance benefit, if it restricts flow (compared to the orginal) you'll get a loss. Most of the posts I've read have either resulted in same performance level or slightly better. To me, putting in the Y and a high flow muffler and some nice dual tips would be more of a sound and visual improvement for my Zetec than a performance one. Where are you having it done (or did you have it done)? Pro Tire & Exhaust in Long Lake does great work. . .