Maybe it's in my head, but I ran premium in my murano for the first 2 years, switched off for a couple of months and thought there was a real drop off in mileage so I switched back to premium (I have no empiricle evidence to back this up).
The real thing that pisses me off isn't the extra cost of the premium, it's how the gas companies keep increasingi the price difference, used to be $.10, then $.11, now $.12 difference at Esso between regular and premium - crooks