3.5" or 4" Downpipe?
 

With a 4" exhaust system, would it be better to go with a 3.5" to 4" downpipe to help spool the turbo faster? Or should I just go 4" all the way? Which would you get? Also, what gauge steel does the aluminized MBRP exhaust systems use? 16 gauge or 14 gauge?

Finally, living in CA, I feel kinda iffy about completely removing the cat when installing a new exhaust. I guess there's nothing to do about it right?