This article was helpful for me.
http://www.imakenews.com/tomballford...bFcFg,bcRJCqRP
and I do think it is a bit rude to tell people who are asking this question they do not need a performance car. There are several reasons for asking what will happen with 87 octane. For instance, if they plan on using recommended but run into a hard time financially unexpectedly, or if They like 400 hp more than 304 but can live with 400 instead of 422 (a decrease but still much better than the V6).
Or more importantly, if they let their sister or father borrow the car and they don't even ask what grade it takes and just fill it up the way they will, The owner will want to know if these people will actually damage their car. I know my father would use 87 even if I told him not to. I am glad to know he will not actually damage my car if I buy the LS3. This is some peace of mind and a good reason to ask this question.
But the price difference per year really isn't that much considering if I drive 10k miles per year (and I do even commuting) then with a car that gets 13/20 (like the LS3 G8 GXP) say I average 17mpg, then with a 30 cent difference, that only equals a total
yearly DIFFERENCE in cost of 176 dollars and forty seven cents. Thats far less than the difference in cost between the 26mpg v6 and the 20mpg v8 just due to fuel economy even if they both used 87.