Well if there was no difference in performance in using premium, why would they recommend it? That would be a silly thing on their part.

I've had all kinds of vehicles in the past, a few with picky motors, such as a '97 Cobra, and a VW New Beetle 1.8L Turbo (also needed premium). Spend time on their forums, you'll hear people fussing about lack of performance on standard gas. Will you notice a difference in daily driving... no. But slam your foot into it, the engine will detect ping (pre-detonation) before you can feel or hear it, and automatically retard the timing. Lots of info about this very topic. So if you plan on getting top performance, premium fuel is a must. If you plan on getting to the mall in rush hour traffic, use the cheap stuff.

You can google this for more info, but here's a clip to back up what I've told you in my previous post:

Answer: Some cars have knock sensors that adjust timing for different grades of fuel and some do not. On cars equipped with a knock sensor and where the manufacturer recommends 91 octane, a lower octane fuel can be tried because the knock sensor will adjust the timing for the lower grade. However, performance and mileage will suffer. Now to your specific car, it most certainly will suffer if you use 87-octane fuel.

Read the full post here.