For your number four I would put N/A maybe, But not when Boosted. Search QTP.

I dont think its rasp as much as gargle...

Here http://www.quicktimeperformance.com/

 

this will warp your exhaust vales like crazy. +1 on the straight through exhaust. It will at least be better than open headers, but sound like crap.

 

This reminds me of the time when my friend hollowed out his cats on his RX7. His exhaust sounded odd, and some nasty smell would get in the car every time he warmed it up. First time I got in his car after he did the mod, "What the hell is that smell? You leaking gas or something?". He ended up having to put on a new cat since he had to get his car smogged and it didn't add any power, but just made it smell like ***.

Moral of the story is: Before you do anything to your car make sure you won't want to undo it. Since it'll probably end up costing you. Especially with the Z costing quite a bit more for repairs/work/parts.