Realistic expectations

I'm 99.9% sure I'll be going w/ a full exhaust swap as my next mod job: 1 5/8" or 1 3/4" MAC longtubes, MAC prochamber (2.5") or h-pipe, and 2.5" cat back. What improvements can I REALISTICALLY expect (hp gain, 1/4 time, sound)????
Thanks for your .02!


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'90 LX 5.0;12K original miles (no sh*&);3.55 gears; March pulleys;Edelbrock Performer Heads;BBK 1 5/8" equal length shorties;MSD 6AL ignition w/ blaster 2 coil;FMS E303 cam;Pro-M 75mm MAF;BBK 70mm TB; Eibach drag-launch spring kit;Southside welded subs;9" K&N cone filter charger;Hurst shifter;Cervini's 3" turbo hood;A/C delete; gutted cats;2 chamber Flomasters;Corbeau racing seats;FMS 30# injectors;JMS chip; Holley 190lb fp;TFS track heat Intake (12.299 @ 113 - 1.78 60')