From what I've heard, you shouldn't put any grade different from what is specified in your car, except in emergencies. i.e., putting premium in Bob's pickup would be just as bad as us putting regular in the Rover. The engines are designed specifically for that grade, and work the best on it.

These days, with the increase in all these ECUs and MFUs in cars, it seems even more important to be careful with your grade. It's something I'll have to look into more...will ask the people on my Land Rover board, who might be able to give some good answers (they live, eat, and breathe this kind of stuff...some even more than me!).

Will get back when I get some good help.