This is how I've always looked at what gas to get...

Super is always about $.20-.25 more than regular. For the LS, it's about $4.83 more per fill (about one grande, super frapamapa lata or whatever at StarBuck). But let's look at over "life" of car and say 200K.

200,000 / (19 mpg avg) = 10,526 gallons x $.23 difference = $2421. If you do 200K in one year, then that's a big hit. If you do that over 10 years, then not so bad at $242/year.

For me, if I had that extra $4/fill, it would go towards a value meal anyway, so I look at it as I'm living healthier with my car...

 

Around here, in Georgia, Super is $.40 more expensive than regular unleaded. That's $7 more per fill.
My car gets the same fuel economy on regular as on super duper. (27-28mpg highway) My car has pretty much the same compression ratio as the 430, yet has less sophisticated engine management and valve timing technology - which means that it's less able to compensate for regular gasoline.
But it runs just fine. I don't notice $7 worth of "umph" with premium gas, and DEFINITELY not enough to justify the 16% premium. So not running the premium is like a "free tank of gas after seven fillups" savings.
YMMV.

 

I bought htis car expecting to meet the manufacturers recommendation. So I do JMO

 

Unless you're running these cars at the drag strip (or driving on the street like you're at a track - but then you'd have a whole different set of problems to worry about) regular gas won't hurt a thing.

 

I once was obsessed with this issue. I read alot online about it. Funny answer I got from some Nasa level engineers: Basically cars like Mercedes, Porche, etc. make cars they recommend you run on premium. They sell these and market them worldwide. Guess what? Premium fuel isn't available in all countries, doh! They don't make cars that wouldn't run in all markets they have a dealership, now would they? These NASA guys opined about the engines, which are tinker toys compared to what they work with, and agreed they can easily adjust to what is given to them.

Only two cars I had that NEEDED premium:

Corvette Z06

64 Ford Thunderbird 429 V8