I am set on getting a Skunk2 Cat Back Exhaust... my issue is the size..

DO i get the 60mm or 70mm? I know the larger the piping the louder the sound (which isnt a big deal as long as it isnt enough to get the cops to bother me)... but am also concerned about back pressure, or lack there of....

I currently have an injen CAI, and will get a high flow cat with the exhaust....and plan on either getting Skunk2 headers down the road or a turbo... with about 6-8psi nothing crazy.

Any advice would be appreciated.

Regards,