145hp is approximately what the factory rating was.
Horsepower wont differ much between aftermarket exhausts. It comes down to 'How loud do you want to get'. Everybody has different exhausts here on the forum but the only problem is, you cant hear them. I used to have just pipe after the cat. No muffler at all and thought it sounded pretty good. But after awhile the sound at speed was getting to be too much. Now I have a Motorsports header with a GReddy muffler I yanked off a Prelude at a junkyard. A little too quiet, but has a nice tone to it. Soon I will take out the cat and replace with a pipe to increase the sound a little, just to see what its like. Also use the replacement pipe for an Air/Fuel ratio meter sensor to get this new engine tuned properly.
I know this didnt specifically answer your question, but truly, there isnt a specific answer. Other than using 2 1/2 pipe, the rest is up to your personal taste.