20BHP sound great. I will also add this to give it atleast 30BHP moore :P
I don't want it to be that much louder, is it such a big differens even on a standard exhaust? I like it quiet as it is standard but I would like a big roar when flooring it :D. That is perhaps hard to achieve?
What should I do, forget about decatting and look for a aftermarket cat back system?