fuel recommendations

LOL. anytime I have ever raised this issue (doesn't matter what car) I get "run the highest $#% you can get your feeble hands on". I understand and I give up. Bottom Line : I'm just trying not to overdo it and waste $ but I do want to give it all that it can use..
thanks

I had a new 383 form S barracuda in 1968, I ran ethel back then, and it was hell of a lot better than 91 or 93 !!