This is one of those eternal debates that have very few definite answers.
My view is:
Try lower octane gas, if you notice either knocking or decreased performance then you should stick with the higher octane fuel.
Try midgrade first, then if everything is good, try regular. My mother had a Mazda Miata that recommended Midgrade but would run fine on Regular.
As far as engine life goes, I believe the extra 'cleaners' in many premium gases amount to a negligible difference in engine life. Other maintenance makes a MUCH larger impact than fuel choice (ala regular oil changes, fuel system maintenance, etc).
I found a PDF article that says the 2005 Crossfire SRT-6 has a compression ratio of 9.0:1 which I believe must be when the supercharger is NOT running. Many of my naturally aspirated cars had that compression ratio or higher and ran on Regular fuel.
I believe that sometimes the recommendations by manufacturers (not just automobile makers) are a best-case scenario. For the absolute best maintenace/performance you should follow their guidelines, but oftentimes 90% of people can't tell any difference between the two maintenance practices.
As a rule of thumb, I put fuel system cleaner through my cars every 5,000 miles to make sure I have clean injectors, fuel pump, et al