I have both. 2010 2SS/RS and a 2006 "Z". Neither of these cars are my DD. My Camaro sits under cover in the garage and the "Z" car sits under cover next to my house. They are both weekend drivers, so neither one takes a lot of abuse.
They are both great cars in their own ways. there are a lot of comments that the "Z" is only a two seater, but realistically, there's not a whole lot of room in the back seat in our 5th gen's either.
My "Z" is a bone stock car and my 5th gen is slightly modified with exhaust and CAI. Although I have not done a side by side "out of the hole" comparison (outside of statistics on paper), I would say that they are pretty close "out of the hole."
The "Z" corners like it's sitting on rails and is great for "canyon carving."
There are pros and cons for both cars. If you're looking for something "zippy" and extremely manueuverable in traffic, the "Z" car is the way to go. Particularly if you don't have family and extra baggage that you need to be concerned about.
Either way, I like both of my cars. If you want "neck snapping" out of the hole response, there's nothing like a true normally aspirated muscle car.
Why not keep the 5th Gen and settle for a 350Z and you can have the best of both worlds!
Just my 2 cents.