We did a little test on the GXP (different engine, I know). The book says it is fine to run regular, but better performance with premium. Over five tanks of gas with each type our mileage was so much better with premium that the differential between regular and premium would have to be about $0.50/gallon to make running regular more economical than premium. We were unable to detect the same difference for the 96 SSE (L36) so always run regular in it, although some people swear their L36'* run better on premium. I don't know if that is true or not.
So if your manual says you will get better performance (and mileage by default) with premium, it will be to your benefit to run premium. But I can see where fuel is a deciding factor. My daily driver is a 92 Nissan with two hamsters and a rubber band- about 32-34 mpg on regular. 0-60 ? Yes, that'* how fast it goes... from 0 to 60.