HP expectation for exaust change?

[911st]

For a 3.2 Carrera, what should the performance expectation be between:

Stock--- cat only---- cat & sport muffler---- full header system?

I am thinking:
10-15p --cat bypass only---------------$200
15-20hp --cat & sport muffler---------$1,000
20-25hp --headers and sport muff---$2,000
25hp-------headers & open or full race exhaust

Assuming a proper tune and chip to match.

I really wonder if there is much to be expected with a added expense of a sport muffler added to the cat delete. (yes, getter looks and sound)

I assume the stock muffler was designed to work with the cat should be good because the cat dose part of the muffling. So the muffler might already be somewhat of a sport muffler.

Anyone made any dyno runs to check. I have seen the 911chips dyno'