It's all swings and roundabouts... JG ran a full NA Miltek system and still hit 258bhp iirc? He is now running a Tullet manifold, Tullet cat (2.5) and a miltek tubby backbox and is at 262bhp (and more noise). I'm running 2.5 piper cat with standard manifold, with a 2.5 2bular backbox and hit 261. Others are running standard cat and even a VSE (goose) and he hit 250bhp. So, go figure!
I was running standard manifold + cat and a regal BB and hit 250