octane/HP rumors?

[rppngears]

I always use 93 octane in my 91 5.0 because I was under the impression that it is better for my engine because of all the detergents it contains. I've run 89 before with no problem, I just usually opt for the 93. After reading this post particularly what prkwud stated I now think I might actually be doing my engine harm. Is this right? Should I use the 89 octane from now on? I'm not trying to get any horsepower gains from using either one, I just want to use whatever is better for my engine. I do have my timing slightly advanced, but like I said there is no knocking when I use 89.