1. Can't comment as I have the 7AT
2. You'll do fine without one
3. g37s is a fancy coupe. Like your Stang' in the sense it has back seats, but isn't a 'sports car' like the 370 is. I'd pick a new Z over a used 911, but thats just me. Consider the warrenty and the like. Atleast with a new Z you know how its been treated from the start, the 911 on the other hand you don't.
4. Go with the Rag top. IMO its one of the best looking verts out there, and from what I've heard some people find that the Nismo is kinda a waste. It sounds like you'll be using the car as a DD so I think you'll have more fun and be more comfortable with a drop top.
So to sum it up, go with a 370 Convertable.
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