Sorry I didn't see your question earlier. I think somebody already responded that $4/gal did hurt Hummer/guzzler sales, which I agree with. To "Kill" the guzzlers, I think it has to be a combination of price and future expectations. If people think gas prices will always roller coaster, its going to be hard to kill the guzzler. But to speculate an answer to your question I will say $6/gallon will kill Hummer, Escalade, and other guzzlers permanently. But I didn't specify how long that price has to stay there. Its longer than 6 months, less than 6 years! I would take a wild-ass guess at it and say if gas hits $6/gallon for 2.5 years, there will be no more guzzlers on the market new. You'll be able to buy used ones forever, but a used Escalade at that point would be worth about the amount you could get for the scrap metal its made of. Could we ever get so lucky as to have this happen? No. As I said my tin-foil hat is gone, and I believe the powers that be, whoever and wherever they are, will never let gas go much higher than $4/gallon, and will never let it stay there for long.
Here's a question for you: if gas prices rose to $5/gallon and stayed there for 2 years (say 2016 - 2018) and showed no sign of decline, what would the resale value of a 2011 Volt be that cost $45k new and has an all-electric range of 30 miles?