I got the 2.5" and dont regret it, bring on the torque i say.
Make sure you get 2 mufflers otherwise it will sound like poop =)
My extactors go in thursday, ill post a sound clip when its all done.
Yes it does well depends which hi flow cats u get! i got the ballistic hi flow racing cats ive been hearing only good things about these cats on the ls1 forum. Chek out the sureflo exhaust website for more info. For the sound i cant explain it relli but sounds better then stock but ye only way to know is by listenin it in real life too bad ur not in nsw... I am very happy wit wat i got.
Afew years back i had pacemaker extractors fitted to a 6cylinder i had while retaining the stock exhaust and it made NO difference in noise.
Also if you are going to get them ceramic coated save some pennies for o2 sensors,i had ceramic coated pacies fitted to my 6 litre and the coatings damaged my o2 sensors,upon doing a search afterwards i found this to be a common problem.