You should the run the engine at the recommended octane for max performance benefit. Higher won't hurt (but unless your tuned for it - a waste of money and zero benefit), lower will hurt your engine.
Eberything You Ever Wanted To Know About Octane
I'm with Spitfiretr7 - Shell is the best. I believe the 370 manual even says to stay away from ethanol fuels. It's just an additive to make gas cheaper but in the end, not as good as pure gas. I know Shell's V power is pure, I thought Petro Can was too.