I have a 04 civic. In the manual it says that i could use 86 or higher octane gas. Lately I have been putting in 93 octane because it feels like it has a very,very,very slight difference in power and it seems like it is less noisy than 87 octane (could be psychological). So I was wondering if there were any benefits of the extra dollar or two that I spend each fillup or am I just wasting my money? Any adverse effects?