Agreed...I also have 2bular GT3 8x24 with 2bular decat - don't need a tune with this. I also have ported header - again don't need tune.If you do header and cat you will need a tune. So its up to you how much you want to spend. Also headers will void your warranty if you still have one. Remember you can still upgrade the headers later on when you decided to tune for more power.
If you go with just 2bular exhaust, it's relatively quiet (just over 100 dbl - when you are WOT - at least, that's what Laguna sound checked me at).
I have Charlie tune with BWR setup.
Nice thing about Jim's 2bulars is that he sets up the exhaust for s/c - just let him know in advance.