Welcome Marco,
We met yesterday. Paul's systems are the best finished I have seen.
As you say yesterday, I have the Viking headers with the Supertrapp muffler. I went that way because I liked the look and sound. Paul's entire system is excellent too.
I also like the Rinehart muffler, but apparently it is no longer available.
You can get the system in satin black or polished aluminium finishes.
Performance will be about the same whether you use the standard muffler or and aftermarket one. Sound will vary depending on the muffler.
Other good systems are made by Reband at Victor Harbor and CES from Queensland.
You should change the air intake at the same time. Ramair and K&N make great replacements that fit under the bear claw. You can remove plenty of plastic and save a bit of weight too.
You are definitely going to need a decent tune. Let me know and I can help.
Plenty of people will be along shortly with their opinions and ideas.