that's at the crank, rwhp would be 10-15 hp. depending on transmission & tune.
the six is really hampered by the intake more than the exhaust, and it has a LESS radical cam than the 94-98s.
The more air you can get into the cylinder, the more power you make.
With the 1.8RRs, you increase the lift a pretty good amount, and a little on the duration as the leverage opens them a little faster.
They're cheaper at www.RPM-Mustangs.com