Yeah you're all totally right, the general rule is that the bigger the exhaust the better as it allows the turbo to start spooling sooner. However under the advice of my mechanic (who has tuned some very amazing race cars and is considered something of an authority in Australia) I was told that due to the twin charge system I will still want to maintain some level of back pressure.
I am certainly no authority and have very limited mechanical knowledge but I would assume that being twin charged would mean that the way the turbo kicks in is slightly different to a normal turbod car as you already have the induction going before the turbo starts spooling, meaning it is more of a feed in style arrangement as opposed to wanting to dump exhaust gas quickly to get the turbo started in the first place. Like i say tho, I'm not mechanically minded enough to be making any arguments for or against I can only go by what others have told me. When I asked Ed about it a while back he said a 2" system and I got the impression my mechanic was looking at about the same size...but I will be getting him to do up my new exhaust in the next couple of months (will prolly book it in the next few weeks) and will gladly share with yas any advice he gives me about it. Until then I'm more than happy to take on any other opinions on the subject as I'm trying to learn as much as i can...but i do appreciate that with any standard turbo car the rule is "the bigger the better" and i understand why that is the case...just want to clarify that i'm not trying to argue with anyone who would most likely know more than I do...I'm just making the point that it isnt a standard turbo induction. cheers