How restrictive is the stock boxster muffler?

[986Porsche986]

I got rid of the stock muffler and put on a top speed muffler.

http://www.topspeedauto.com/ProductCart/pc/viewPrd.asp?idcategory=0&idproduct=1781

I really like the sound and that the top speed muffler is lighter and it doesn't turn my rear trunk into an oven. However, It seems to me that the car did lose some hp. I am going to run my iphone application "dynolicious" on the two mufflers and check my suspicions sometime in the next few months.