Those were the days when premium was only 0.20 more per gallon, but it is not the case anymore. I don't know when it changed, but I'm guessing at least 10-15 years ago and is now anywhere from 0.60 to 0.80 more per gallon. As an example at Marathon right now it is 3.08 for regular and 3.74 for premium. I would have no problem paying 0.20 more per gallon, but 0.66 is way too much difference IMO. Plus if it isn't hurting your engine and you may lose say 5-10hp that you probably won't even notice. That is a substantial savings over time if you fill up several times a month. Now if I were going to the track and wanted to get every tenth, then I would wait until near empty and fill up with premium a few days before that way you can get the maximum hp.