I had the exact same setup on my 1994 GT, so let me share my experience. Bottom line, the most power will come from the H. I left the tailpipes stock when I put in the flows, and when I switched over after the H, the difference was more than I expected. I had a local muffler shop make me 2.5" tails out of my mufflers, and that alone uncorked some lost power from the H. After that, I put in MAC equal length shorties, and they mainly killed my idle and some of my low end, but bumped my midrange a bit. They also changed the note of my exhaust a bit. I can't say for sure that it was the headers that killed my idle, but my idle was never the same afterwards. The install was shady, so it was probably installed incorrectly (not sealed). After all was said and done, here is my theory:
Get the H if you want sound and HP on a budget.
Don't pay for the entire cat back from Flowmaster; your local Muffler shop will do it for a fraction of the price.
Think carefully about header choice. Equals are just as hard to put in as Long tubes, and the gains are slight. Unequals give almost as much for cheaper and easier install.
Overall, with your setup, you will gain probably 20rwhp.
I installed flowtech unequal length headers just the cheapys and bbk hi flow catted h pipe. I also installed the cai at the same time but it was like a whole new car. Nice meaty sound. Mine idle's great. It will actually break the tires loose in second gear now without abusing it. The headers slipped right in no problems. Then I bumped the timing up to 14* now amazing. Good luck Great first bolt ons. I have since installed the items on my sig.