ZERO
IMO, unless you want to be "the first kid on the block with the newest toy", there is absolutely NO reason to pay above sticker.
When I was getting ready to buy the SS, I shopped several dealers, and just about all of them tried to explain the mark-up as a "by-product" of wanting a car that had to be "ordered".
So, I just took my time, shopped via the internet, and ended up getting the SS under sticker.
Same thing occured to my brother when he was buying his C6.
As I said, unless you "gotta have it" immediately, if you're willing to do some "homework", and wait a little, you can get the car at sticker.