The offer I got from Tesla was 17% off full invoice (not including state sales taxes) and a reduction of 1% per month. For ease of math on a non-sig it was something like $100K minus $17K minus $6K or $77K net.
I suspect the MB dealership would be much more brutal should you choose to return your S-Class after five months. It is never cheap to consume the new car smell.
Like fiksegts, I too did much better on the secondary market although I think he did much better than me
On a side note, I've taken the Sig and early delivery MS experiences and tried to learn from them. Mission Motors is coming out with what I feel is the first real electric super bike and it is everything I can do not to put down a deposit for delivery next year. It would seem the wise decision on these things is to let the dust settle, be patient and pick one up after they have been shipping for a few months. Man that's hard.