bwcobra15 is right, premium is a waste of money. As he said, high compression is usually the only reason to run a higher octane (at least, on a factory stock motor) & our 4.6 only has around 9.5:1 compression (I can't remember the actual rating). As a comparison, I own a 1970 Monte Carlo with a 402 with 10.25:1 compression & I rarely run anything other than 87 octane. The only time I notice a power difference is on cool mornings or evenings with little humidity. So, if a high compression, 30 year old big block runs fine on 87, so will our new small blocks.